[v5] kasan: unify kasan_enabled() and remove arch-specific implementations

[PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Sabyrzhan Tasbolatov 1 month, 4 weeks ago

Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
to defer KASAN initialization until shadow memory is properly set up,
and unify the static key infrastructure across all KASAN modes.

[1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
Changes in v5:
- Unified patches where arch (powerpc, UML, loongarch) selects
  ARCH_DEFER_KASAN in the first patch not to break
  bisectability
- Removed kasan_arch_is_ready completely as there is no user
- Removed __wrappers in v4, left only those where it's necessary
  due to different implementations

Changes in v4:
- Fixed HW_TAGS static key functionality (was broken in v3)
- Merged configuration and implementation for atomicity
---
 arch/loongarch/Kconfig                 |  1 +
 arch/loongarch/include/asm/kasan.h     |  7 ------
 arch/loongarch/mm/kasan_init.c         |  8 +++----
 arch/powerpc/Kconfig                   |  1 +
 arch/powerpc/include/asm/kasan.h       | 12 ----------
 arch/powerpc/mm/kasan/init_32.c        |  2 +-
 arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
 arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
 arch/um/Kconfig                        |  1 +
 arch/um/include/asm/kasan.h            |  5 ++--
 arch/um/kernel/mem.c                   | 10 ++++++--
 include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
 include/linux/kasan.h                  |  6 +++++
 lib/Kconfig.kasan                      |  8 +++++++
 mm/kasan/common.c                      | 17 ++++++++++----
 mm/kasan/generic.c                     | 19 +++++++++++----
 mm/kasan/hw_tags.c                     |  9 +-------
 mm/kasan/kasan.h                       |  8 ++++++-
 mm/kasan/shadow.c                      | 12 +++++-----
 mm/kasan/sw_tags.c                     |  1 +
 mm/kasan/tags.c                        |  2 +-
 21 files changed, 100 insertions(+), 69 deletions(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index f0abc38c40a..cd64b2bc12d 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -9,6 +9,7 @@ config LOONGARCH
 	select ACPI_PPTT if ACPI
 	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
 	select ARCH_BINFMT_ELF_STATE
+	select ARCH_DEFER_KASAN if KASAN
 	select ARCH_DISABLE_KASAN_INLINE
 	select ARCH_ENABLE_MEMORY_HOTPLUG
 	select ARCH_ENABLE_MEMORY_HOTREMOVE
diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
index 62f139a9c87..0e50e5b5e05 100644
--- a/arch/loongarch/include/asm/kasan.h
+++ b/arch/loongarch/include/asm/kasan.h
@@ -66,7 +66,6 @@
 #define XKPRANGE_WC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
 #define XKVRANGE_VC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
 
-extern bool kasan_early_stage;
 extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
 
 #define kasan_mem_to_shadow kasan_mem_to_shadow
@@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
 #define kasan_shadow_to_mem kasan_shadow_to_mem
 const void *kasan_shadow_to_mem(const void *shadow_addr);
 
-#define kasan_arch_is_ready kasan_arch_is_ready
-static __always_inline bool kasan_arch_is_ready(void)
-{
-	return !kasan_early_stage;
-}
-
 #define addr_has_metadata addr_has_metadata
 static __always_inline bool addr_has_metadata(const void *addr)
 {
diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index d2681272d8f..170da98ad4f 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
 #define __pte_none(early, pte) (early ? pte_none(pte) : \
 ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
 
-bool kasan_early_stage = true;
-
 void *kasan_mem_to_shadow(const void *addr)
 {
-	if (!kasan_arch_is_ready()) {
+	if (!kasan_enabled()) {
 		return (void *)(kasan_early_shadow_page);
 	} else {
 		unsigned long maddr = (unsigned long)addr;
@@ -298,7 +296,8 @@ void __init kasan_init(void)
 	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
 					kasan_mem_to_shadow((void *)KFENCE_AREA_END));
 
-	kasan_early_stage = false;
+	/* Enable KASAN here before kasan_mem_to_shadow(). */
+	kasan_init_generic();
 
 	/* Populate the linear mapping */
 	for_each_mem_range(i, &pa_start, &pa_end) {
@@ -329,5 +328,4 @@ void __init kasan_init(void)
 
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
-	pr_info("KernelAddressSanitizer initialized.\n");
 }
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 93402a1d9c9..a324dcdb8eb 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -122,6 +122,7 @@ config PPC
 	# Please keep this list sorted alphabetically.
 	#
 	select ARCH_32BIT_OFF_T if PPC32
+	select ARCH_DEFER_KASAN			if KASAN && PPC_RADIX_MMU
 	select ARCH_DISABLE_KASAN_INLINE	if PPC_RADIX_MMU
 	select ARCH_DMA_DEFAULT_COHERENT	if !NOT_COHERENT_CACHE
 	select ARCH_ENABLE_MEMORY_HOTPLUG
diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
index b5bbb94c51f..957a57c1db5 100644
--- a/arch/powerpc/include/asm/kasan.h
+++ b/arch/powerpc/include/asm/kasan.h
@@ -53,18 +53,6 @@
 #endif
 
 #ifdef CONFIG_KASAN
-#ifdef CONFIG_PPC_BOOK3S_64
-DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
-
-static __always_inline bool kasan_arch_is_ready(void)
-{
-	if (static_branch_likely(&powerpc_kasan_enabled_key))
-		return true;
-	return false;
-}
-
-#define kasan_arch_is_ready kasan_arch_is_ready
-#endif
 
 void kasan_early_init(void);
 void kasan_mmu_init(void);
diff --git a/arch/powerpc/mm/kasan/init_32.c b/arch/powerpc/mm/kasan/init_32.c
index 03666d790a5..1d083597464 100644
--- a/arch/powerpc/mm/kasan/init_32.c
+++ b/arch/powerpc/mm/kasan/init_32.c
@@ -165,7 +165,7 @@ void __init kasan_init(void)
 
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
-	pr_info("KASAN init done\n");
+	kasan_init_generic();
 }
 
 void __init kasan_late_init(void)
diff --git a/arch/powerpc/mm/kasan/init_book3e_64.c b/arch/powerpc/mm/kasan/init_book3e_64.c
index 60c78aac0f6..0d3a73d6d4b 100644
--- a/arch/powerpc/mm/kasan/init_book3e_64.c
+++ b/arch/powerpc/mm/kasan/init_book3e_64.c
@@ -127,7 +127,7 @@ void __init kasan_init(void)
 
 	/* Enable error messages */
 	init_task.kasan_depth = 0;
-	pr_info("KASAN init done\n");
+	kasan_init_generic();
 }
 
 void __init kasan_late_init(void) { }
diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
index 7d959544c07..dcafa641804 100644
--- a/arch/powerpc/mm/kasan/init_book3s_64.c
+++ b/arch/powerpc/mm/kasan/init_book3s_64.c
@@ -19,8 +19,6 @@
 #include <linux/memblock.h>
 #include <asm/pgalloc.h>
 
-DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
-
 static void __init kasan_init_phys_region(void *start, void *end)
 {
 	unsigned long k_start, k_end, k_cur;
@@ -92,11 +90,9 @@ void __init kasan_init(void)
 	 */
 	memset(kasan_early_shadow_page, 0, PAGE_SIZE);
 
-	static_branch_inc(&powerpc_kasan_enabled_key);
-
 	/* Enable error messages */
 	init_task.kasan_depth = 0;
-	pr_info("KASAN init done\n");
+	kasan_init_generic();
 }
 
 void __init kasan_early_init(void) { }
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 9083bfdb773..a12cc072ab1 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -5,6 +5,7 @@ menu "UML-specific options"
 config UML
 	bool
 	default y
+	select ARCH_DEFER_KASAN if STATIC_LINK
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_HAS_CACHE_LINE_SIZE
 	select ARCH_HAS_CPU_FINALIZE_INIT
diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
index f97bb1f7b85..b54a4e937fd 100644
--- a/arch/um/include/asm/kasan.h
+++ b/arch/um/include/asm/kasan.h
@@ -24,10 +24,9 @@
 
 #ifdef CONFIG_KASAN
 void kasan_init(void);
-extern int kasan_um_is_ready;
 
-#ifdef CONFIG_STATIC_LINK
-#define kasan_arch_is_ready() (kasan_um_is_ready)
+#if defined(CONFIG_STATIC_LINK) && defined(CONFIG_KASAN_INLINE)
+#error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!
 #endif
 #else
 static inline void kasan_init(void) { }
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index 76bec7de81b..261fdcd21be 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -21,9 +21,9 @@
 #include <os.h>
 #include <um_malloc.h>
 #include <linux/sched/task.h>
+#include <linux/kasan.h>
 
 #ifdef CONFIG_KASAN
-int kasan_um_is_ready;
 void kasan_init(void)
 {
 	/*
@@ -32,7 +32,10 @@ void kasan_init(void)
 	 */
 	kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
 	init_task.kasan_depth = 0;
-	kasan_um_is_ready = true;
+	/* Since kasan_init() is called before main(),
+	 * KASAN is initialized but the enablement is deferred after
+	 * jump_label_init(). See arch_mm_preinit().
+	 */
 }
 
 static void (*kasan_init_ptr)(void)
@@ -58,6 +61,9 @@ static unsigned long brk_end;
 
 void __init arch_mm_preinit(void)
 {
+	/* Safe to call after jump_label_init(). Enables KASAN. */
+	kasan_init_generic();
+
 	/* clear the zero-page */
 	memset(empty_zero_page, 0, PAGE_SIZE);
 
diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
index 6f612d69ea0..9eca967d852 100644
--- a/include/linux/kasan-enabled.h
+++ b/include/linux/kasan-enabled.h
@@ -4,32 +4,46 @@
 
 #include <linux/static_key.h>
 
-#ifdef CONFIG_KASAN_HW_TAGS
-
+#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
+/*
+ * Global runtime flag for KASAN modes that need runtime control.
+ * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
+ */
 DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
 
+/*
+ * Runtime control for shadow memory initialization or HW_TAGS mode.
+ * Uses static key for architectures that need deferred KASAN or HW_TAGS.
+ */
 static __always_inline bool kasan_enabled(void)
 {
 	return static_branch_likely(&kasan_flag_enabled);
 }
 
-static inline bool kasan_hw_tags_enabled(void)
+static inline void kasan_enable(void)
 {
-	return kasan_enabled();
+	static_branch_enable(&kasan_flag_enabled);
 }
-
-#else /* CONFIG_KASAN_HW_TAGS */
-
-static inline bool kasan_enabled(void)
+#else
+/* For architectures that can enable KASAN early, use compile-time check. */
+static __always_inline bool kasan_enabled(void)
 {
 	return IS_ENABLED(CONFIG_KASAN);
 }
 
+static inline void kasan_enable(void) {}
+#endif /* CONFIG_ARCH_DEFER_KASAN || CONFIG_KASAN_HW_TAGS */
+
+#ifdef CONFIG_KASAN_HW_TAGS
+static inline bool kasan_hw_tags_enabled(void)
+{
+	return kasan_enabled();
+}
+#else
 static inline bool kasan_hw_tags_enabled(void)
 {
 	return false;
 }
-
 #endif /* CONFIG_KASAN_HW_TAGS */
 
 #endif /* LINUX_KASAN_ENABLED_H */
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 890011071f2..51a8293d1af 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -543,6 +543,12 @@ void kasan_report_async(void);
 
 #endif /* CONFIG_KASAN_HW_TAGS */
 
+#ifdef CONFIG_KASAN_GENERIC
+void __init kasan_init_generic(void);
+#else
+static inline void kasan_init_generic(void) { }
+#endif
+
 #ifdef CONFIG_KASAN_SW_TAGS
 void __init kasan_init_sw_tags(void);
 #else
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f82889a830f..38456560c85 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
 	  Disables both inline and stack instrumentation. Selected by
 	  architectures that do not support these instrumentation types.
 
+config ARCH_DEFER_KASAN
+	bool
+	help
+	  Architectures should select this if they need to defer KASAN
+	  initialization until shadow memory is properly set up. This
+	  enables runtime control via static keys. Otherwise, KASAN uses
+	  compile-time constants for better performance.
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 9142964ab9c..d9d389870a2 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -32,6 +32,15 @@
 #include "kasan.h"
 #include "../slab.h"
 
+#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
+/*
+ * Definition of the unified static key declared in kasan-enabled.h.
+ * This provides consistent runtime enable/disable across KASAN modes.
+ */
+DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
+EXPORT_SYMBOL(kasan_flag_enabled);
+#endif
+
 struct slab *kasan_addr_to_slab(const void *addr)
 {
 	if (virt_addr_valid(addr))
@@ -246,7 +255,7 @@ static inline void poison_slab_object(struct kmem_cache *cache, void *object,
 bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
 				unsigned long ip)
 {
-	if (!kasan_arch_is_ready() || is_kfence_address(object))
+	if (is_kfence_address(object))
 		return false;
 	return check_slab_allocation(cache, object, ip);
 }
@@ -254,7 +263,7 @@ bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
 bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
 		       bool still_accessible)
 {
-	if (!kasan_arch_is_ready() || is_kfence_address(object))
+	if (is_kfence_address(object))
 		return false;
 
 	/*
@@ -293,7 +302,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
 
 static inline bool check_page_allocation(void *ptr, unsigned long ip)
 {
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return false;
 
 	if (ptr != page_address(virt_to_head_page(ptr))) {
@@ -522,7 +531,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 		return true;
 	}
 
-	if (is_kfence_address(ptr) || !kasan_arch_is_ready())
+	if (is_kfence_address(ptr))
 		return true;
 
 	slab = folio_slab(folio);
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index d54e89f8c3e..b413c46b3e0 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -36,6 +36,17 @@
 #include "kasan.h"
 #include "../slab.h"
 
+/*
+ * Initialize Generic KASAN and enable runtime checks.
+ * This should be called from arch kasan_init() once shadow memory is ready.
+ */
+void __init kasan_init_generic(void)
+{
+	kasan_enable();
+
+	pr_info("KernelAddressSanitizer initialized (generic)\n");
+}
+
 /*
  * All functions below always inlined so compiler could
  * perform better optimizations in each of __asan_loadX/__assn_storeX
@@ -165,7 +176,7 @@ static __always_inline bool check_region_inline(const void *addr,
 						size_t size, bool write,
 						unsigned long ret_ip)
 {
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return true;
 
 	if (unlikely(size == 0))
@@ -193,7 +204,7 @@ bool kasan_byte_accessible(const void *addr)
 {
 	s8 shadow_byte;
 
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return true;
 
 	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
@@ -495,7 +506,7 @@ static void release_alloc_meta(struct kasan_alloc_meta *meta)
 
 static void release_free_meta(const void *object, struct kasan_free_meta *meta)
 {
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return;
 
 	/* Check if free meta is valid. */
@@ -562,7 +573,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
 	kasan_save_track(&alloc_meta->alloc_track, flags);
 }
 
-void kasan_save_free_info(struct kmem_cache *cache, void *object)
+void __kasan_save_free_info(struct kmem_cache *cache, void *object)
 {
 	struct kasan_free_meta *free_meta;
 
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 9a6927394b5..c8289a3feab 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -45,13 +45,6 @@ static enum kasan_arg kasan_arg __ro_after_init;
 static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
 static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
 
-/*
- * Whether KASAN is enabled at all.
- * The value remains false until KASAN is initialized by kasan_init_hw_tags().
- */
-DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
-EXPORT_SYMBOL(kasan_flag_enabled);
-
 /*
  * Whether the selected mode is synchronous, asynchronous, or asymmetric.
  * Defaults to KASAN_MODE_SYNC.
@@ -260,7 +253,7 @@ void __init kasan_init_hw_tags(void)
 	kasan_init_tags();
 
 	/* KASAN is now initialized, enable it. */
-	static_branch_enable(&kasan_flag_enabled);
+	kasan_enable();
 
 	pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
 		kasan_mode_info(),
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 129178be5e6..8a9d8a6ea71 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -398,7 +398,13 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
 void kasan_set_track(struct kasan_track *track, depot_stack_handle_t stack);
 void kasan_save_track(struct kasan_track *track, gfp_t flags);
 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
-void kasan_save_free_info(struct kmem_cache *cache, void *object);
+
+void __kasan_save_free_info(struct kmem_cache *cache, void *object);
+static inline void kasan_save_free_info(struct kmem_cache *cache, void *object)
+{
+	if (kasan_enabled())
+		__kasan_save_free_info(cache, object);
+}
 
 #ifdef CONFIG_KASAN_GENERIC
 bool kasan_quarantine_put(struct kmem_cache *cache, void *object);
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index d2c70cd2afb..2e126cb21b6 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -125,7 +125,7 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
 {
 	void *shadow_start, *shadow_end;
 
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return;
 
 	/*
@@ -150,7 +150,7 @@ EXPORT_SYMBOL_GPL(kasan_poison);
 #ifdef CONFIG_KASAN_GENERIC
 void kasan_poison_last_granule(const void *addr, size_t size)
 {
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return;
 
 	if (size & KASAN_GRANULE_MASK) {
@@ -390,7 +390,7 @@ int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
 	unsigned long shadow_start, shadow_end;
 	int ret;
 
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return 0;
 
 	if (!is_vmalloc_or_module_addr((void *)addr))
@@ -560,7 +560,7 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 	unsigned long region_start, region_end;
 	unsigned long size;
 
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return;
 
 	region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
@@ -611,7 +611,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 	 * with setting memory tags, so the KASAN_VMALLOC_INIT flag is ignored.
 	 */
 
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return (void *)start;
 
 	if (!is_vmalloc_or_module_addr(start))
@@ -636,7 +636,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
  */
 void __kasan_poison_vmalloc(const void *start, unsigned long size)
 {
-	if (!kasan_arch_is_ready())
+	if (!kasan_enabled())
 		return;
 
 	if (!is_vmalloc_or_module_addr(start))
diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
index b9382b5b6a3..c75741a7460 100644
--- a/mm/kasan/sw_tags.c
+++ b/mm/kasan/sw_tags.c
@@ -44,6 +44,7 @@ void __init kasan_init_sw_tags(void)
 		per_cpu(prng_state, cpu) = (u32)get_cycles();
 
 	kasan_init_tags();
+	kasan_enable();
 
 	pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n",
 		str_on_off(kasan_stack_collection_enabled()));
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index d65d48b85f9..b9f31293622 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -142,7 +142,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
 	save_stack_info(cache, object, flags, false);
 }
 
-void kasan_save_free_info(struct kmem_cache *cache, void *object)
+void __kasan_save_free_info(struct kmem_cache *cache, void *object)
 {
 	save_stack_info(cache, object, 0, true);
 }
-- 
2.34.1

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Christophe Leroy 1 month, 4 weeks ago


Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> to defer KASAN initialization until shadow memory is properly set up,
> and unify the static key infrastructure across all KASAN modes.

That probably desserves more details, maybe copy in informations from 
the top of cover letter.

I think there should also be some exeplanations about 
kasan_arch_is_ready() becoming kasan_enabled(), and also why 
kasan_arch_is_ready() completely disappear from mm/kasan/common.c 
without being replaced by kasan_enabled().

> 
> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> 
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
> Changes in v5:
> - Unified patches where arch (powerpc, UML, loongarch) selects
>    ARCH_DEFER_KASAN in the first patch not to break
>    bisectability
> - Removed kasan_arch_is_ready completely as there is no user
> - Removed __wrappers in v4, left only those where it's necessary
>    due to different implementations
> 
> Changes in v4:
> - Fixed HW_TAGS static key functionality (was broken in v3)
> - Merged configuration and implementation for atomicity
> ---
>   arch/loongarch/Kconfig                 |  1 +
>   arch/loongarch/include/asm/kasan.h     |  7 ------
>   arch/loongarch/mm/kasan_init.c         |  8 +++----
>   arch/powerpc/Kconfig                   |  1 +
>   arch/powerpc/include/asm/kasan.h       | 12 ----------
>   arch/powerpc/mm/kasan/init_32.c        |  2 +-
>   arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
>   arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
>   arch/um/Kconfig                        |  1 +
>   arch/um/include/asm/kasan.h            |  5 ++--
>   arch/um/kernel/mem.c                   | 10 ++++++--
>   include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
>   include/linux/kasan.h                  |  6 +++++
>   lib/Kconfig.kasan                      |  8 +++++++
>   mm/kasan/common.c                      | 17 ++++++++++----
>   mm/kasan/generic.c                     | 19 +++++++++++----
>   mm/kasan/hw_tags.c                     |  9 +-------
>   mm/kasan/kasan.h                       |  8 ++++++-
>   mm/kasan/shadow.c                      | 12 +++++-----
>   mm/kasan/sw_tags.c                     |  1 +
>   mm/kasan/tags.c                        |  2 +-
>   21 files changed, 100 insertions(+), 69 deletions(-)
> 
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index f0abc38c40a..cd64b2bc12d 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -9,6 +9,7 @@ config LOONGARCH
>   	select ACPI_PPTT if ACPI
>   	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
>   	select ARCH_BINFMT_ELF_STATE
> +	select ARCH_DEFER_KASAN if KASAN

Instead of adding 'if KASAN' in all users, you could do in two steps:

Add a symbol ARCH_NEEDS_DEFER_KASAN.

+config ARCH_NEEDS_DEFER_KASAN
+	bool

And then:

+config ARCH_DEFER_KASAN
+	def_bool
+	depends on KASAN
+	depends on ARCH_DEFER_KASAN
+	help
+	  Architectures should select this if they need to defer KASAN
+	  initialization until shadow memory is properly set up. This
+	  enables runtime control via static keys. Otherwise, KASAN uses
+	  compile-time constants for better performance.



>   	select ARCH_DISABLE_KASAN_INLINE
>   	select ARCH_ENABLE_MEMORY_HOTPLUG
>   	select ARCH_ENABLE_MEMORY_HOTREMOVE
> diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
> index 62f139a9c87..0e50e5b5e05 100644
> --- a/arch/loongarch/include/asm/kasan.h
> +++ b/arch/loongarch/include/asm/kasan.h
> @@ -66,7 +66,6 @@
>   #define XKPRANGE_WC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
>   #define XKVRANGE_VC_SHADOW_OFFSET	(KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
>   
> -extern bool kasan_early_stage;
>   extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
>   
>   #define kasan_mem_to_shadow kasan_mem_to_shadow
> @@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
>   #define kasan_shadow_to_mem kasan_shadow_to_mem
>   const void *kasan_shadow_to_mem(const void *shadow_addr);
>   
> -#define kasan_arch_is_ready kasan_arch_is_ready
> -static __always_inline bool kasan_arch_is_ready(void)
> -{
> -	return !kasan_early_stage;
> -}
> -
>   #define addr_has_metadata addr_has_metadata
>   static __always_inline bool addr_has_metadata(const void *addr)
>   {
> diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> index d2681272d8f..170da98ad4f 100644
> --- a/arch/loongarch/mm/kasan_init.c
> +++ b/arch/loongarch/mm/kasan_init.c
> @@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>   #define __pte_none(early, pte) (early ? pte_none(pte) : \
>   ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
>   
> -bool kasan_early_stage = true;
> -
>   void *kasan_mem_to_shadow(const void *addr)
>   {
> -	if (!kasan_arch_is_ready()) {
> +	if (!kasan_enabled()) {
>   		return (void *)(kasan_early_shadow_page);
>   	} else {
>   		unsigned long maddr = (unsigned long)addr;
> @@ -298,7 +296,8 @@ void __init kasan_init(void)
>   	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
>   					kasan_mem_to_shadow((void *)KFENCE_AREA_END));
>   
> -	kasan_early_stage = false;
> +	/* Enable KASAN here before kasan_mem_to_shadow(). */
> +	kasan_init_generic();
>   
>   	/* Populate the linear mapping */
>   	for_each_mem_range(i, &pa_start, &pa_end) {
> @@ -329,5 +328,4 @@ void __init kasan_init(void)
>   
>   	/* At this point kasan is fully initialized. Enable error messages */
>   	init_task.kasan_depth = 0;
> -	pr_info("KernelAddressSanitizer initialized.\n");
>   }
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 93402a1d9c9..a324dcdb8eb 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -122,6 +122,7 @@ config PPC
>   	# Please keep this list sorted alphabetically.
>   	#
>   	select ARCH_32BIT_OFF_T if PPC32
> +	select ARCH_DEFER_KASAN			if KASAN && PPC_RADIX_MMU
>   	select ARCH_DISABLE_KASAN_INLINE	if PPC_RADIX_MMU
>   	select ARCH_DMA_DEFAULT_COHERENT	if !NOT_COHERENT_CACHE
>   	select ARCH_ENABLE_MEMORY_HOTPLUG
> diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> index b5bbb94c51f..957a57c1db5 100644
> --- a/arch/powerpc/include/asm/kasan.h
> +++ b/arch/powerpc/include/asm/kasan.h
> @@ -53,18 +53,6 @@
>   #endif
>   
>   #ifdef CONFIG_KASAN
> -#ifdef CONFIG_PPC_BOOK3S_64
> -DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> -
> -static __always_inline bool kasan_arch_is_ready(void)
> -{
> -	if (static_branch_likely(&powerpc_kasan_enabled_key))
> -		return true;
> -	return false;
> -}
> -
> -#define kasan_arch_is_ready kasan_arch_is_ready
> -#endif
>   
>   void kasan_early_init(void);
>   void kasan_mmu_init(void);
> diff --git a/arch/powerpc/mm/kasan/init_32.c b/arch/powerpc/mm/kasan/init_32.c
> index 03666d790a5..1d083597464 100644
> --- a/arch/powerpc/mm/kasan/init_32.c
> +++ b/arch/powerpc/mm/kasan/init_32.c
> @@ -165,7 +165,7 @@ void __init kasan_init(void)
>   
>   	/* At this point kasan is fully initialized. Enable error messages */
>   	init_task.kasan_depth = 0;
> -	pr_info("KASAN init done\n");
> +	kasan_init_generic();
>   }
>   
>   void __init kasan_late_init(void)
> diff --git a/arch/powerpc/mm/kasan/init_book3e_64.c b/arch/powerpc/mm/kasan/init_book3e_64.c
> index 60c78aac0f6..0d3a73d6d4b 100644
> --- a/arch/powerpc/mm/kasan/init_book3e_64.c
> +++ b/arch/powerpc/mm/kasan/init_book3e_64.c
> @@ -127,7 +127,7 @@ void __init kasan_init(void)
>   
>   	/* Enable error messages */
>   	init_task.kasan_depth = 0;
> -	pr_info("KASAN init done\n");
> +	kasan_init_generic();
>   }
>   
>   void __init kasan_late_init(void) { }
> diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
> index 7d959544c07..dcafa641804 100644
> --- a/arch/powerpc/mm/kasan/init_book3s_64.c
> +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
> @@ -19,8 +19,6 @@
>   #include <linux/memblock.h>
>   #include <asm/pgalloc.h>
>   
> -DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> -
>   static void __init kasan_init_phys_region(void *start, void *end)
>   {
>   	unsigned long k_start, k_end, k_cur;
> @@ -92,11 +90,9 @@ void __init kasan_init(void)
>   	 */
>   	memset(kasan_early_shadow_page, 0, PAGE_SIZE);
>   
> -	static_branch_inc(&powerpc_kasan_enabled_key);
> -
>   	/* Enable error messages */
>   	init_task.kasan_depth = 0;
> -	pr_info("KASAN init done\n");
> +	kasan_init_generic();
>   }
>   
>   void __init kasan_early_init(void) { }
> diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> index 9083bfdb773..a12cc072ab1 100644
> --- a/arch/um/Kconfig
> +++ b/arch/um/Kconfig
> @@ -5,6 +5,7 @@ menu "UML-specific options"
>   config UML
>   	bool
>   	default y
> +	select ARCH_DEFER_KASAN if STATIC_LINK

No need to also verify KASAN here like powerpc and loongarch ?

>   	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
>   	select ARCH_HAS_CACHE_LINE_SIZE
>   	select ARCH_HAS_CPU_FINALIZE_INIT
> diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
> index f97bb1f7b85..b54a4e937fd 100644
> --- a/arch/um/include/asm/kasan.h
> +++ b/arch/um/include/asm/kasan.h
> @@ -24,10 +24,9 @@
>   
>   #ifdef CONFIG_KASAN
>   void kasan_init(void);
> -extern int kasan_um_is_ready;
>   
> -#ifdef CONFIG_STATIC_LINK
> -#define kasan_arch_is_ready() (kasan_um_is_ready)
> +#if defined(CONFIG_STATIC_LINK) && defined(CONFIG_KASAN_INLINE)
> +#error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!
>   #endif
>   #else
>   static inline void kasan_init(void) { }
> diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
> index 76bec7de81b..261fdcd21be 100644
> --- a/arch/um/kernel/mem.c
> +++ b/arch/um/kernel/mem.c
> @@ -21,9 +21,9 @@
>   #include <os.h>
>   #include <um_malloc.h>
>   #include <linux/sched/task.h>
> +#include <linux/kasan.h>
>   
>   #ifdef CONFIG_KASAN
> -int kasan_um_is_ready;
>   void kasan_init(void)
>   {
>   	/*
> @@ -32,7 +32,10 @@ void kasan_init(void)
>   	 */
>   	kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
>   	init_task.kasan_depth = 0;
> -	kasan_um_is_ready = true;
> +	/* Since kasan_init() is called before main(),
> +	 * KASAN is initialized but the enablement is deferred after
> +	 * jump_label_init(). See arch_mm_preinit().
> +	 */

Format standard is different outside network, see: 
https://docs.kernel.org/process/coding-style.html#commenting

>   }
>   
>   static void (*kasan_init_ptr)(void)
> @@ -58,6 +61,9 @@ static unsigned long brk_end;
>   
>   void __init arch_mm_preinit(void)
>   {
> +	/* Safe to call after jump_label_init(). Enables KASAN. */
> +	kasan_init_generic();
> +
>   	/* clear the zero-page */
>   	memset(empty_zero_page, 0, PAGE_SIZE);
>   
> diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> index 6f612d69ea0..9eca967d852 100644
> --- a/include/linux/kasan-enabled.h
> +++ b/include/linux/kasan-enabled.h
> @@ -4,32 +4,46 @@
>   
>   #include <linux/static_key.h>
>   
> -#ifdef CONFIG_KASAN_HW_TAGS
> -
> +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> +/*
> + * Global runtime flag for KASAN modes that need runtime control.
> + * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
> + */
>   DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
>   
> +/*
> + * Runtime control for shadow memory initialization or HW_TAGS mode.
> + * Uses static key for architectures that need deferred KASAN or HW_TAGS.
> + */
>   static __always_inline bool kasan_enabled(void)
>   {
>   	return static_branch_likely(&kasan_flag_enabled);
>   }
>   
> -static inline bool kasan_hw_tags_enabled(void)
> +static inline void kasan_enable(void)
>   {
> -	return kasan_enabled();
> +	static_branch_enable(&kasan_flag_enabled);
>   }
> -
> -#else /* CONFIG_KASAN_HW_TAGS */
> -
> -static inline bool kasan_enabled(void)
> +#else
> +/* For architectures that can enable KASAN early, use compile-time check. */
> +static __always_inline bool kasan_enabled(void)
>   {
>   	return IS_ENABLED(CONFIG_KASAN);
>   }
>   
> +static inline void kasan_enable(void) {}
> +#endif /* CONFIG_ARCH_DEFER_KASAN || CONFIG_KASAN_HW_TAGS */
> +
> +#ifdef CONFIG_KASAN_HW_TAGS
> +static inline bool kasan_hw_tags_enabled(void)
> +{
> +	return kasan_enabled();
> +}
> +#else
>   static inline bool kasan_hw_tags_enabled(void)
>   {
>   	return false;
>   }
> -
>   #endif /* CONFIG_KASAN_HW_TAGS */
>   
>   #endif /* LINUX_KASAN_ENABLED_H */
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 890011071f2..51a8293d1af 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -543,6 +543,12 @@ void kasan_report_async(void);
>   
>   #endif /* CONFIG_KASAN_HW_TAGS */
>   
> +#ifdef CONFIG_KASAN_GENERIC
> +void __init kasan_init_generic(void);
> +#else
> +static inline void kasan_init_generic(void) { }
> +#endif
> +
>   #ifdef CONFIG_KASAN_SW_TAGS
>   void __init kasan_init_sw_tags(void);
>   #else
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index f82889a830f..38456560c85 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
>   	  Disables both inline and stack instrumentation. Selected by
>   	  architectures that do not support these instrumentation types.
>   
> +config ARCH_DEFER_KASAN
> +	bool
> +	help
> +	  Architectures should select this if they need to defer KASAN
> +	  initialization until shadow memory is properly set up. This
> +	  enables runtime control via static keys. Otherwise, KASAN uses
> +	  compile-time constants for better performance.
> +
>   config CC_HAS_KASAN_GENERIC
>   	def_bool $(cc-option, -fsanitize=kernel-address)
>   
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 9142964ab9c..d9d389870a2 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -32,6 +32,15 @@
>   #include "kasan.h"
>   #include "../slab.h"
>   
> +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> +/*
> + * Definition of the unified static key declared in kasan-enabled.h.
> + * This provides consistent runtime enable/disable across KASAN modes.
> + */
> +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> +EXPORT_SYMBOL(kasan_flag_enabled);

Shouldn't new exports be GPL ?

> +#endif
> +
>   struct slab *kasan_addr_to_slab(const void *addr)
>   {
>   	if (virt_addr_valid(addr))
> @@ -246,7 +255,7 @@ static inline void poison_slab_object(struct kmem_cache *cache, void *object,
>   bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
>   				unsigned long ip)
>   {
> -	if (!kasan_arch_is_ready() || is_kfence_address(object))
> +	if (is_kfence_address(object))

Here and below, no need to replace kasan_arch_is_ready() by 
kasan_enabled() ?

>   		return false;
>   	return check_slab_allocation(cache, object, ip);
>   }
> @@ -254,7 +263,7 @@ bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
>   bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
>   		       bool still_accessible)
>   {
> -	if (!kasan_arch_is_ready() || is_kfence_address(object))
> +	if (is_kfence_address(object))
>   		return false;
>   
>   	/*
> @@ -293,7 +302,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
>   
>   static inline bool check_page_allocation(void *ptr, unsigned long ip)
>   {
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return false;
>   
>   	if (ptr != page_address(virt_to_head_page(ptr))) {
> @@ -522,7 +531,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
>   		return true;
>   	}
>   
> -	if (is_kfence_address(ptr) || !kasan_arch_is_ready())
> +	if (is_kfence_address(ptr))
>   		return true;
>   
>   	slab = folio_slab(folio);
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index d54e89f8c3e..b413c46b3e0 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -36,6 +36,17 @@
>   #include "kasan.h"
>   #include "../slab.h"
>   
> +/*
> + * Initialize Generic KASAN and enable runtime checks.
> + * This should be called from arch kasan_init() once shadow memory is ready.
> + */
> +void __init kasan_init_generic(void)
> +{
> +	kasan_enable();
> +
> +	pr_info("KernelAddressSanitizer initialized (generic)\n");
> +}
> +
>   /*
>    * All functions below always inlined so compiler could
>    * perform better optimizations in each of __asan_loadX/__assn_storeX
> @@ -165,7 +176,7 @@ static __always_inline bool check_region_inline(const void *addr,
>   						size_t size, bool write,
>   						unsigned long ret_ip)
>   {
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return true;
>   
>   	if (unlikely(size == 0))
> @@ -193,7 +204,7 @@ bool kasan_byte_accessible(const void *addr)
>   {
>   	s8 shadow_byte;
>   
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return true;
>   
>   	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
> @@ -495,7 +506,7 @@ static void release_alloc_meta(struct kasan_alloc_meta *meta)
>   
>   static void release_free_meta(const void *object, struct kasan_free_meta *meta)
>   {
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return;
>   
>   	/* Check if free meta is valid. */
> @@ -562,7 +573,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
>   	kasan_save_track(&alloc_meta->alloc_track, flags);
>   }
>   
> -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
>   {
>   	struct kasan_free_meta *free_meta;
>   
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 9a6927394b5..c8289a3feab 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -45,13 +45,6 @@ static enum kasan_arg kasan_arg __ro_after_init;
>   static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
>   static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
>   
> -/*
> - * Whether KASAN is enabled at all.
> - * The value remains false until KASAN is initialized by kasan_init_hw_tags().
> - */
> -DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> -EXPORT_SYMBOL(kasan_flag_enabled);
> -
>   /*
>    * Whether the selected mode is synchronous, asynchronous, or asymmetric.
>    * Defaults to KASAN_MODE_SYNC.
> @@ -260,7 +253,7 @@ void __init kasan_init_hw_tags(void)
>   	kasan_init_tags();
>   
>   	/* KASAN is now initialized, enable it. */
> -	static_branch_enable(&kasan_flag_enabled);
> +	kasan_enable();
>   
>   	pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
>   		kasan_mode_info(),
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 129178be5e6..8a9d8a6ea71 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -398,7 +398,13 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
>   void kasan_set_track(struct kasan_track *track, depot_stack_handle_t stack);
>   void kasan_save_track(struct kasan_track *track, gfp_t flags);
>   void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
> -void kasan_save_free_info(struct kmem_cache *cache, void *object);
> +
> +void __kasan_save_free_info(struct kmem_cache *cache, void *object);
> +static inline void kasan_save_free_info(struct kmem_cache *cache, void *object)
> +{
> +	if (kasan_enabled())
> +		__kasan_save_free_info(cache, object);
> +}
>   
>   #ifdef CONFIG_KASAN_GENERIC
>   bool kasan_quarantine_put(struct kmem_cache *cache, void *object);
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index d2c70cd2afb..2e126cb21b6 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -125,7 +125,7 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
>   {
>   	void *shadow_start, *shadow_end;
>   
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return;
>   
>   	/*
> @@ -150,7 +150,7 @@ EXPORT_SYMBOL_GPL(kasan_poison);
>   #ifdef CONFIG_KASAN_GENERIC
>   void kasan_poison_last_granule(const void *addr, size_t size)
>   {
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return;
>   
>   	if (size & KASAN_GRANULE_MASK) {
> @@ -390,7 +390,7 @@ int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
>   	unsigned long shadow_start, shadow_end;
>   	int ret;
>   
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return 0;
>   
>   	if (!is_vmalloc_or_module_addr((void *)addr))
> @@ -560,7 +560,7 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>   	unsigned long region_start, region_end;
>   	unsigned long size;
>   
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return;
>   
>   	region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
> @@ -611,7 +611,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
>   	 * with setting memory tags, so the KASAN_VMALLOC_INIT flag is ignored.
>   	 */
>   
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return (void *)start;
>   
>   	if (!is_vmalloc_or_module_addr(start))
> @@ -636,7 +636,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
>    */
>   void __kasan_poison_vmalloc(const void *start, unsigned long size)
>   {
> -	if (!kasan_arch_is_ready())
> +	if (!kasan_enabled())
>   		return;
>   
>   	if (!is_vmalloc_or_module_addr(start))
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index b9382b5b6a3..c75741a7460 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -44,6 +44,7 @@ void __init kasan_init_sw_tags(void)
>   		per_cpu(prng_state, cpu) = (u32)get_cycles();
>   
>   	kasan_init_tags();
> +	kasan_enable();
>   
>   	pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n",
>   		str_on_off(kasan_stack_collection_enabled()));
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index d65d48b85f9..b9f31293622 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -142,7 +142,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
>   	save_stack_info(cache, object, flags, false);
>   }
>   
> -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
>   {
>   	save_stack_info(cache, object, 0, true);
>   }

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Sabyrzhan Tasbolatov 1 month, 3 weeks ago

On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> > Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> > to defer KASAN initialization until shadow memory is properly set up,
> > and unify the static key infrastructure across all KASAN modes.
>
> That probably desserves more details, maybe copy in informations from
> the top of cover letter.
>
> I think there should also be some exeplanations about
> kasan_arch_is_ready() becoming kasan_enabled(), and also why
> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
> without being replaced by kasan_enabled().
>
> >
> > [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> >
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> > ---
> > Changes in v5:
> > - Unified patches where arch (powerpc, UML, loongarch) selects
> >    ARCH_DEFER_KASAN in the first patch not to break
> >    bisectability
> > - Removed kasan_arch_is_ready completely as there is no user
> > - Removed __wrappers in v4, left only those where it's necessary
> >    due to different implementations
> >
> > Changes in v4:
> > - Fixed HW_TAGS static key functionality (was broken in v3)
> > - Merged configuration and implementation for atomicity
> > ---
> >   arch/loongarch/Kconfig                 |  1 +
> >   arch/loongarch/include/asm/kasan.h     |  7 ------
> >   arch/loongarch/mm/kasan_init.c         |  8 +++----
> >   arch/powerpc/Kconfig                   |  1 +
> >   arch/powerpc/include/asm/kasan.h       | 12 ----------
> >   arch/powerpc/mm/kasan/init_32.c        |  2 +-
> >   arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
> >   arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
> >   arch/um/Kconfig                        |  1 +
> >   arch/um/include/asm/kasan.h            |  5 ++--
> >   arch/um/kernel/mem.c                   | 10 ++++++--
> >   include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
> >   include/linux/kasan.h                  |  6 +++++
> >   lib/Kconfig.kasan                      |  8 +++++++
> >   mm/kasan/common.c                      | 17 ++++++++++----
> >   mm/kasan/generic.c                     | 19 +++++++++++----
> >   mm/kasan/hw_tags.c                     |  9 +-------
> >   mm/kasan/kasan.h                       |  8 ++++++-
> >   mm/kasan/shadow.c                      | 12 +++++-----
> >   mm/kasan/sw_tags.c                     |  1 +
> >   mm/kasan/tags.c                        |  2 +-
> >   21 files changed, 100 insertions(+), 69 deletions(-)
> >
> > diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > index f0abc38c40a..cd64b2bc12d 100644
> > --- a/arch/loongarch/Kconfig
> > +++ b/arch/loongarch/Kconfig
> > @@ -9,6 +9,7 @@ config LOONGARCH
> >       select ACPI_PPTT if ACPI
> >       select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> >       select ARCH_BINFMT_ELF_STATE
> > +     select ARCH_DEFER_KASAN if KASAN
>
> Instead of adding 'if KASAN' in all users, you could do in two steps:
>
> Add a symbol ARCH_NEEDS_DEFER_KASAN.
>
> +config ARCH_NEEDS_DEFER_KASAN
> +       bool
>
> And then:
>
> +config ARCH_DEFER_KASAN
> +       def_bool
> +       depends on KASAN
> +       depends on ARCH_DEFER_KASAN
> +       help
> +         Architectures should select this if they need to defer KASAN
> +         initialization until shadow memory is properly set up. This
> +         enables runtime control via static keys. Otherwise, KASAN uses
> +         compile-time constants for better performance.
>

Actually, I don't see the benefits from this option. Sorry, have just
revisited this again.
With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
2 options:

select ARCH_NEEDS_DEFER_KASAN
select ARCH_DEFER_KASAN

and the oneline with `if` condition is cleaner.
select ARCH_DEFER_KASAN if KASAN

>
>
> >       select ARCH_DISABLE_KASAN_INLINE
> >       select ARCH_ENABLE_MEMORY_HOTPLUG
> >       select ARCH_ENABLE_MEMORY_HOTREMOVE
> > diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
> > index 62f139a9c87..0e50e5b5e05 100644
> > --- a/arch/loongarch/include/asm/kasan.h
> > +++ b/arch/loongarch/include/asm/kasan.h
> > @@ -66,7 +66,6 @@
> >   #define XKPRANGE_WC_SHADOW_OFFSET   (KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
> >   #define XKVRANGE_VC_SHADOW_OFFSET   (KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
> >
> > -extern bool kasan_early_stage;
> >   extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
> >
> >   #define kasan_mem_to_shadow kasan_mem_to_shadow
> > @@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
> >   #define kasan_shadow_to_mem kasan_shadow_to_mem
> >   const void *kasan_shadow_to_mem(const void *shadow_addr);
> >
> > -#define kasan_arch_is_ready kasan_arch_is_ready
> > -static __always_inline bool kasan_arch_is_ready(void)
> > -{
> > -     return !kasan_early_stage;
> > -}
> > -
> >   #define addr_has_metadata addr_has_metadata
> >   static __always_inline bool addr_has_metadata(const void *addr)
> >   {
> > diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> > index d2681272d8f..170da98ad4f 100644
> > --- a/arch/loongarch/mm/kasan_init.c
> > +++ b/arch/loongarch/mm/kasan_init.c
> > @@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> >   #define __pte_none(early, pte) (early ? pte_none(pte) : \
> >   ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
> >
> > -bool kasan_early_stage = true;
> > -
> >   void *kasan_mem_to_shadow(const void *addr)
> >   {
> > -     if (!kasan_arch_is_ready()) {
> > +     if (!kasan_enabled()) {
> >               return (void *)(kasan_early_shadow_page);
> >       } else {
> >               unsigned long maddr = (unsigned long)addr;
> > @@ -298,7 +296,8 @@ void __init kasan_init(void)
> >       kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> >                                       kasan_mem_to_shadow((void *)KFENCE_AREA_END));
> >
> > -     kasan_early_stage = false;
> > +     /* Enable KASAN here before kasan_mem_to_shadow(). */
> > +     kasan_init_generic();
> >
> >       /* Populate the linear mapping */
> >       for_each_mem_range(i, &pa_start, &pa_end) {
> > @@ -329,5 +328,4 @@ void __init kasan_init(void)
> >
> >       /* At this point kasan is fully initialized. Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KernelAddressSanitizer initialized.\n");
> >   }
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 93402a1d9c9..a324dcdb8eb 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -122,6 +122,7 @@ config PPC
> >       # Please keep this list sorted alphabetically.
> >       #
> >       select ARCH_32BIT_OFF_T if PPC32
> > +     select ARCH_DEFER_KASAN                 if KASAN && PPC_RADIX_MMU
> >       select ARCH_DISABLE_KASAN_INLINE        if PPC_RADIX_MMU
> >       select ARCH_DMA_DEFAULT_COHERENT        if !NOT_COHERENT_CACHE
> >       select ARCH_ENABLE_MEMORY_HOTPLUG
> > diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> > index b5bbb94c51f..957a57c1db5 100644
> > --- a/arch/powerpc/include/asm/kasan.h
> > +++ b/arch/powerpc/include/asm/kasan.h
> > @@ -53,18 +53,6 @@
> >   #endif
> >
> >   #ifdef CONFIG_KASAN
> > -#ifdef CONFIG_PPC_BOOK3S_64
> > -DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> > -
> > -static __always_inline bool kasan_arch_is_ready(void)
> > -{
> > -     if (static_branch_likely(&powerpc_kasan_enabled_key))
> > -             return true;
> > -     return false;
> > -}
> > -
> > -#define kasan_arch_is_ready kasan_arch_is_ready
> > -#endif
> >
> >   void kasan_early_init(void);
> >   void kasan_mmu_init(void);
> > diff --git a/arch/powerpc/mm/kasan/init_32.c b/arch/powerpc/mm/kasan/init_32.c
> > index 03666d790a5..1d083597464 100644
> > --- a/arch/powerpc/mm/kasan/init_32.c
> > +++ b/arch/powerpc/mm/kasan/init_32.c
> > @@ -165,7 +165,7 @@ void __init kasan_init(void)
> >
> >       /* At this point kasan is fully initialized. Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_late_init(void)
> > diff --git a/arch/powerpc/mm/kasan/init_book3e_64.c b/arch/powerpc/mm/kasan/init_book3e_64.c
> > index 60c78aac0f6..0d3a73d6d4b 100644
> > --- a/arch/powerpc/mm/kasan/init_book3e_64.c
> > +++ b/arch/powerpc/mm/kasan/init_book3e_64.c
> > @@ -127,7 +127,7 @@ void __init kasan_init(void)
> >
> >       /* Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_late_init(void) { }
> > diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
> > index 7d959544c07..dcafa641804 100644
> > --- a/arch/powerpc/mm/kasan/init_book3s_64.c
> > +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
> > @@ -19,8 +19,6 @@
> >   #include <linux/memblock.h>
> >   #include <asm/pgalloc.h>
> >
> > -DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> > -
> >   static void __init kasan_init_phys_region(void *start, void *end)
> >   {
> >       unsigned long k_start, k_end, k_cur;
> > @@ -92,11 +90,9 @@ void __init kasan_init(void)
> >        */
> >       memset(kasan_early_shadow_page, 0, PAGE_SIZE);
> >
> > -     static_branch_inc(&powerpc_kasan_enabled_key);
> > -
> >       /* Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_early_init(void) { }
> > diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> > index 9083bfdb773..a12cc072ab1 100644
> > --- a/arch/um/Kconfig
> > +++ b/arch/um/Kconfig
> > @@ -5,6 +5,7 @@ menu "UML-specific options"
> >   config UML
> >       bool
> >       default y
> > +     select ARCH_DEFER_KASAN if STATIC_LINK
>
> No need to also verify KASAN here like powerpc and loongarch ?
>
> >       select ARCH_WANTS_DYNAMIC_TASK_STRUCT
> >       select ARCH_HAS_CACHE_LINE_SIZE
> >       select ARCH_HAS_CPU_FINALIZE_INIT
> > diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
> > index f97bb1f7b85..b54a4e937fd 100644
> > --- a/arch/um/include/asm/kasan.h
> > +++ b/arch/um/include/asm/kasan.h
> > @@ -24,10 +24,9 @@
> >
> >   #ifdef CONFIG_KASAN
> >   void kasan_init(void);
> > -extern int kasan_um_is_ready;
> >
> > -#ifdef CONFIG_STATIC_LINK
> > -#define kasan_arch_is_ready() (kasan_um_is_ready)
> > +#if defined(CONFIG_STATIC_LINK) && defined(CONFIG_KASAN_INLINE)
> > +#error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!
> >   #endif
> >   #else
> >   static inline void kasan_init(void) { }
> > diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
> > index 76bec7de81b..261fdcd21be 100644
> > --- a/arch/um/kernel/mem.c
> > +++ b/arch/um/kernel/mem.c
> > @@ -21,9 +21,9 @@
> >   #include <os.h>
> >   #include <um_malloc.h>
> >   #include <linux/sched/task.h>
> > +#include <linux/kasan.h>
> >
> >   #ifdef CONFIG_KASAN
> > -int kasan_um_is_ready;
> >   void kasan_init(void)
> >   {
> >       /*
> > @@ -32,7 +32,10 @@ void kasan_init(void)
> >        */
> >       kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
> >       init_task.kasan_depth = 0;
> > -     kasan_um_is_ready = true;
> > +     /* Since kasan_init() is called before main(),
> > +      * KASAN is initialized but the enablement is deferred after
> > +      * jump_label_init(). See arch_mm_preinit().
> > +      */
>
> Format standard is different outside network, see:
> https://docs.kernel.org/process/coding-style.html#commenting
>
> >   }
> >
> >   static void (*kasan_init_ptr)(void)
> > @@ -58,6 +61,9 @@ static unsigned long brk_end;
> >
> >   void __init arch_mm_preinit(void)
> >   {
> > +     /* Safe to call after jump_label_init(). Enables KASAN. */
> > +     kasan_init_generic();
> > +
> >       /* clear the zero-page */
> >       memset(empty_zero_page, 0, PAGE_SIZE);
> >
> > diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> > index 6f612d69ea0..9eca967d852 100644
> > --- a/include/linux/kasan-enabled.h
> > +++ b/include/linux/kasan-enabled.h
> > @@ -4,32 +4,46 @@
> >
> >   #include <linux/static_key.h>
> >
> > -#ifdef CONFIG_KASAN_HW_TAGS
> > -
> > +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> > +/*
> > + * Global runtime flag for KASAN modes that need runtime control.
> > + * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
> > + */
> >   DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> >
> > +/*
> > + * Runtime control for shadow memory initialization or HW_TAGS mode.
> > + * Uses static key for architectures that need deferred KASAN or HW_TAGS.
> > + */
> >   static __always_inline bool kasan_enabled(void)
> >   {
> >       return static_branch_likely(&kasan_flag_enabled);
> >   }
> >
> > -static inline bool kasan_hw_tags_enabled(void)
> > +static inline void kasan_enable(void)
> >   {
> > -     return kasan_enabled();
> > +     static_branch_enable(&kasan_flag_enabled);
> >   }
> > -
> > -#else /* CONFIG_KASAN_HW_TAGS */
> > -
> > -static inline bool kasan_enabled(void)
> > +#else
> > +/* For architectures that can enable KASAN early, use compile-time check. */
> > +static __always_inline bool kasan_enabled(void)
> >   {
> >       return IS_ENABLED(CONFIG_KASAN);
> >   }
> >
> > +static inline void kasan_enable(void) {}
> > +#endif /* CONFIG_ARCH_DEFER_KASAN || CONFIG_KASAN_HW_TAGS */
> > +
> > +#ifdef CONFIG_KASAN_HW_TAGS
> > +static inline bool kasan_hw_tags_enabled(void)
> > +{
> > +     return kasan_enabled();
> > +}
> > +#else
> >   static inline bool kasan_hw_tags_enabled(void)
> >   {
> >       return false;
> >   }
> > -
> >   #endif /* CONFIG_KASAN_HW_TAGS */
> >
> >   #endif /* LINUX_KASAN_ENABLED_H */
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index 890011071f2..51a8293d1af 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -543,6 +543,12 @@ void kasan_report_async(void);
> >
> >   #endif /* CONFIG_KASAN_HW_TAGS */
> >
> > +#ifdef CONFIG_KASAN_GENERIC
> > +void __init kasan_init_generic(void);
> > +#else
> > +static inline void kasan_init_generic(void) { }
> > +#endif
> > +
> >   #ifdef CONFIG_KASAN_SW_TAGS
> >   void __init kasan_init_sw_tags(void);
> >   #else
> > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> > index f82889a830f..38456560c85 100644
> > --- a/lib/Kconfig.kasan
> > +++ b/lib/Kconfig.kasan
> > @@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
> >         Disables both inline and stack instrumentation. Selected by
> >         architectures that do not support these instrumentation types.
> >
> > +config ARCH_DEFER_KASAN
> > +     bool
> > +     help
> > +       Architectures should select this if they need to defer KASAN
> > +       initialization until shadow memory is properly set up. This
> > +       enables runtime control via static keys. Otherwise, KASAN uses
> > +       compile-time constants for better performance.
> > +
> >   config CC_HAS_KASAN_GENERIC
> >       def_bool $(cc-option, -fsanitize=kernel-address)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 9142964ab9c..d9d389870a2 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -32,6 +32,15 @@
> >   #include "kasan.h"
> >   #include "../slab.h"
> >
> > +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> > +/*
> > + * Definition of the unified static key declared in kasan-enabled.h.
> > + * This provides consistent runtime enable/disable across KASAN modes.
> > + */
> > +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> > +EXPORT_SYMBOL(kasan_flag_enabled);
>
> Shouldn't new exports be GPL ?
>
> > +#endif
> > +
> >   struct slab *kasan_addr_to_slab(const void *addr)
> >   {
> >       if (virt_addr_valid(addr))
> > @@ -246,7 +255,7 @@ static inline void poison_slab_object(struct kmem_cache *cache, void *object,
> >   bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
> >                               unsigned long ip)
> >   {
> > -     if (!kasan_arch_is_ready() || is_kfence_address(object))
> > +     if (is_kfence_address(object))
>
> Here and below, no need to replace kasan_arch_is_ready() by
> kasan_enabled() ?
>
> >               return false;
> >       return check_slab_allocation(cache, object, ip);
> >   }
> > @@ -254,7 +263,7 @@ bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
> >   bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
> >                      bool still_accessible)
> >   {
> > -     if (!kasan_arch_is_ready() || is_kfence_address(object))
> > +     if (is_kfence_address(object))
> >               return false;
> >
> >       /*
> > @@ -293,7 +302,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
> >
> >   static inline bool check_page_allocation(void *ptr, unsigned long ip)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return false;
> >
> >       if (ptr != page_address(virt_to_head_page(ptr))) {
> > @@ -522,7 +531,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
> >               return true;
> >       }
> >
> > -     if (is_kfence_address(ptr) || !kasan_arch_is_ready())
> > +     if (is_kfence_address(ptr))
> >               return true;
> >
> >       slab = folio_slab(folio);
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index d54e89f8c3e..b413c46b3e0 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -36,6 +36,17 @@
> >   #include "kasan.h"
> >   #include "../slab.h"
> >
> > +/*
> > + * Initialize Generic KASAN and enable runtime checks.
> > + * This should be called from arch kasan_init() once shadow memory is ready.
> > + */
> > +void __init kasan_init_generic(void)
> > +{
> > +     kasan_enable();
> > +
> > +     pr_info("KernelAddressSanitizer initialized (generic)\n");
> > +}
> > +
> >   /*
> >    * All functions below always inlined so compiler could
> >    * perform better optimizations in each of __asan_loadX/__assn_storeX
> > @@ -165,7 +176,7 @@ static __always_inline bool check_region_inline(const void *addr,
> >                                               size_t size, bool write,
> >                                               unsigned long ret_ip)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return true;
> >
> >       if (unlikely(size == 0))
> > @@ -193,7 +204,7 @@ bool kasan_byte_accessible(const void *addr)
> >   {
> >       s8 shadow_byte;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return true;
> >
> >       shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
> > @@ -495,7 +506,7 @@ static void release_alloc_meta(struct kasan_alloc_meta *meta)
> >
> >   static void release_free_meta(const void *object, struct kasan_free_meta *meta)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       /* Check if free meta is valid. */
> > @@ -562,7 +573,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> >       kasan_save_track(&alloc_meta->alloc_track, flags);
> >   }
> >
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
> >   {
> >       struct kasan_free_meta *free_meta;
> >
> > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> > index 9a6927394b5..c8289a3feab 100644
> > --- a/mm/kasan/hw_tags.c
> > +++ b/mm/kasan/hw_tags.c
> > @@ -45,13 +45,6 @@ static enum kasan_arg kasan_arg __ro_after_init;
> >   static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
> >   static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
> >
> > -/*
> > - * Whether KASAN is enabled at all.
> > - * The value remains false until KASAN is initialized by kasan_init_hw_tags().
> > - */
> > -DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> > -EXPORT_SYMBOL(kasan_flag_enabled);
> > -
> >   /*
> >    * Whether the selected mode is synchronous, asynchronous, or asymmetric.
> >    * Defaults to KASAN_MODE_SYNC.
> > @@ -260,7 +253,7 @@ void __init kasan_init_hw_tags(void)
> >       kasan_init_tags();
> >
> >       /* KASAN is now initialized, enable it. */
> > -     static_branch_enable(&kasan_flag_enabled);
> > +     kasan_enable();
> >
> >       pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
> >               kasan_mode_info(),
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index 129178be5e6..8a9d8a6ea71 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -398,7 +398,13 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
> >   void kasan_set_track(struct kasan_track *track, depot_stack_handle_t stack);
> >   void kasan_save_track(struct kasan_track *track, gfp_t flags);
> >   void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object);
> > +
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object);
> > +static inline void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +{
> > +     if (kasan_enabled())
> > +             __kasan_save_free_info(cache, object);
> > +}
> >
> >   #ifdef CONFIG_KASAN_GENERIC
> >   bool kasan_quarantine_put(struct kmem_cache *cache, void *object);
> > diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> > index d2c70cd2afb..2e126cb21b6 100644
> > --- a/mm/kasan/shadow.c
> > +++ b/mm/kasan/shadow.c
> > @@ -125,7 +125,7 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
> >   {
> >       void *shadow_start, *shadow_end;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       /*
> > @@ -150,7 +150,7 @@ EXPORT_SYMBOL_GPL(kasan_poison);
> >   #ifdef CONFIG_KASAN_GENERIC
> >   void kasan_poison_last_granule(const void *addr, size_t size)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       if (size & KASAN_GRANULE_MASK) {
> > @@ -390,7 +390,7 @@ int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
> >       unsigned long shadow_start, shadow_end;
> >       int ret;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return 0;
> >
> >       if (!is_vmalloc_or_module_addr((void *)addr))
> > @@ -560,7 +560,7 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
> >       unsigned long region_start, region_end;
> >       unsigned long size;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
> > @@ -611,7 +611,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> >        * with setting memory tags, so the KASAN_VMALLOC_INIT flag is ignored.
> >        */
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return (void *)start;
> >
> >       if (!is_vmalloc_or_module_addr(start))
> > @@ -636,7 +636,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> >    */
> >   void __kasan_poison_vmalloc(const void *start, unsigned long size)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       if (!is_vmalloc_or_module_addr(start))
> > diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> > index b9382b5b6a3..c75741a7460 100644
> > --- a/mm/kasan/sw_tags.c
> > +++ b/mm/kasan/sw_tags.c
> > @@ -44,6 +44,7 @@ void __init kasan_init_sw_tags(void)
> >               per_cpu(prng_state, cpu) = (u32)get_cycles();
> >
> >       kasan_init_tags();
> > +     kasan_enable();
> >
> >       pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n",
> >               str_on_off(kasan_stack_collection_enabled()));
> > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> > index d65d48b85f9..b9f31293622 100644
> > --- a/mm/kasan/tags.c
> > +++ b/mm/kasan/tags.c
> > @@ -142,7 +142,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> >       save_stack_info(cache, object, flags, false);
> >   }
> >
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
> >   {
> >       save_stack_info(cache, object, 0, true);
> >   }
>

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Christophe Leroy 1 month, 3 weeks ago


Le 08/08/2025 à 17:33, Sabyrzhan Tasbolatov a écrit :
> On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>>
>>
>>
>> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
>>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
>>> to defer KASAN initialization until shadow memory is properly set up,
>>> and unify the static key infrastructure across all KASAN modes.
>>
>> That probably desserves more details, maybe copy in informations from
>> the top of cover letter.
>>
>> I think there should also be some exeplanations about
>> kasan_arch_is_ready() becoming kasan_enabled(), and also why
>> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
>> without being replaced by kasan_enabled().
>>
>>>
>>> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
>>>
>>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D217049&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe4f5a759ad6452b047408ddd691024a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638902640503259176%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UM4uvQihJdeWwcC6DIiJXbn4wGsrijjRcHc55uCMErI%3D&reserved=0
>>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
>>> ---
>>> Changes in v5:
>>> - Unified patches where arch (powerpc, UML, loongarch) selects
>>>     ARCH_DEFER_KASAN in the first patch not to break
>>>     bisectability
>>> - Removed kasan_arch_is_ready completely as there is no user
>>> - Removed __wrappers in v4, left only those where it's necessary
>>>     due to different implementations
>>>
>>> Changes in v4:
>>> - Fixed HW_TAGS static key functionality (was broken in v3)
>>> - Merged configuration and implementation for atomicity
>>> ---
>>>    arch/loongarch/Kconfig                 |  1 +
>>>    arch/loongarch/include/asm/kasan.h     |  7 ------
>>>    arch/loongarch/mm/kasan_init.c         |  8 +++----
>>>    arch/powerpc/Kconfig                   |  1 +
>>>    arch/powerpc/include/asm/kasan.h       | 12 ----------
>>>    arch/powerpc/mm/kasan/init_32.c        |  2 +-
>>>    arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
>>>    arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
>>>    arch/um/Kconfig                        |  1 +
>>>    arch/um/include/asm/kasan.h            |  5 ++--
>>>    arch/um/kernel/mem.c                   | 10 ++++++--
>>>    include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
>>>    include/linux/kasan.h                  |  6 +++++
>>>    lib/Kconfig.kasan                      |  8 +++++++
>>>    mm/kasan/common.c                      | 17 ++++++++++----
>>>    mm/kasan/generic.c                     | 19 +++++++++++----
>>>    mm/kasan/hw_tags.c                     |  9 +-------
>>>    mm/kasan/kasan.h                       |  8 ++++++-
>>>    mm/kasan/shadow.c                      | 12 +++++-----
>>>    mm/kasan/sw_tags.c                     |  1 +
>>>    mm/kasan/tags.c                        |  2 +-
>>>    21 files changed, 100 insertions(+), 69 deletions(-)
>>>
>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>> index f0abc38c40a..cd64b2bc12d 100644
>>> --- a/arch/loongarch/Kconfig
>>> +++ b/arch/loongarch/Kconfig
>>> @@ -9,6 +9,7 @@ config LOONGARCH
>>>        select ACPI_PPTT if ACPI
>>>        select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
>>>        select ARCH_BINFMT_ELF_STATE
>>> +     select ARCH_DEFER_KASAN if KASAN
>>
>> Instead of adding 'if KASAN' in all users, you could do in two steps:
>>
>> Add a symbol ARCH_NEEDS_DEFER_KASAN.
>>
>> +config ARCH_NEEDS_DEFER_KASAN
>> +       bool
>>
>> And then:
>>
>> +config ARCH_DEFER_KASAN
>> +       def_bool
>> +       depends on KASAN
>> +       depends on ARCH_DEFER_KASAN
>> +       help
>> +         Architectures should select this if they need to defer KASAN
>> +         initialization until shadow memory is properly set up. This
>> +         enables runtime control via static keys. Otherwise, KASAN uses
>> +         compile-time constants for better performance.
>>
> 
> Actually, I don't see the benefits from this option. Sorry, have just
> revisited this again.
> With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
> 2 options:
> 
> select ARCH_NEEDS_DEFER_KASAN
> select ARCH_DEFER_KASAN

Sorry, my mistake, ARCH_DEFER_KASAN has to be 'def_bool y'. Missing the 
'y'. That way it is automatically set to 'y' as long as KASAN and 
ARCH_NEEDS_DEFER_KASAN are selected. Should be:

config ARCH_DEFER_KASAN
	def_bool y
	depends on KASAN
	depends on ARCH_NEEDS_DEFER_KASAN


> 
> and the oneline with `if` condition is cleaner.
> select ARCH_DEFER_KASAN if KASAN
> 

I don't think so because it requires all architectures to add 'if KASAN' 
which is not convenient.

Christophe

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Sabyrzhan Tasbolatov 1 month, 3 weeks ago

On Fri, Aug 8, 2025 at 10:03 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 08/08/2025 à 17:33, Sabyrzhan Tasbolatov a écrit :
> > On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> > <christophe.leroy@csgroup.eu> wrote:
> >>
> >>
> >>
> >> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> >>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> >>> to defer KASAN initialization until shadow memory is properly set up,
> >>> and unify the static key infrastructure across all KASAN modes.
> >>
> >> That probably desserves more details, maybe copy in informations from
> >> the top of cover letter.
> >>
> >> I think there should also be some exeplanations about
> >> kasan_arch_is_ready() becoming kasan_enabled(), and also why
> >> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
> >> without being replaced by kasan_enabled().
> >>
> >>>
> >>> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> >>>
> >>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D217049&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe4f5a759ad6452b047408ddd691024a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638902640503259176%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UM4uvQihJdeWwcC6DIiJXbn4wGsrijjRcHc55uCMErI%3D&reserved=0
> >>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> >>> ---
> >>> Changes in v5:
> >>> - Unified patches where arch (powerpc, UML, loongarch) selects
> >>>     ARCH_DEFER_KASAN in the first patch not to break
> >>>     bisectability
> >>> - Removed kasan_arch_is_ready completely as there is no user
> >>> - Removed __wrappers in v4, left only those where it's necessary
> >>>     due to different implementations
> >>>
> >>> Changes in v4:
> >>> - Fixed HW_TAGS static key functionality (was broken in v3)
> >>> - Merged configuration and implementation for atomicity
> >>> ---
> >>>    arch/loongarch/Kconfig                 |  1 +
> >>>    arch/loongarch/include/asm/kasan.h     |  7 ------
> >>>    arch/loongarch/mm/kasan_init.c         |  8 +++----
> >>>    arch/powerpc/Kconfig                   |  1 +
> >>>    arch/powerpc/include/asm/kasan.h       | 12 ----------
> >>>    arch/powerpc/mm/kasan/init_32.c        |  2 +-
> >>>    arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
> >>>    arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
> >>>    arch/um/Kconfig                        |  1 +
> >>>    arch/um/include/asm/kasan.h            |  5 ++--
> >>>    arch/um/kernel/mem.c                   | 10 ++++++--
> >>>    include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
> >>>    include/linux/kasan.h                  |  6 +++++
> >>>    lib/Kconfig.kasan                      |  8 +++++++
> >>>    mm/kasan/common.c                      | 17 ++++++++++----
> >>>    mm/kasan/generic.c                     | 19 +++++++++++----
> >>>    mm/kasan/hw_tags.c                     |  9 +-------
> >>>    mm/kasan/kasan.h                       |  8 ++++++-
> >>>    mm/kasan/shadow.c                      | 12 +++++-----
> >>>    mm/kasan/sw_tags.c                     |  1 +
> >>>    mm/kasan/tags.c                        |  2 +-
> >>>    21 files changed, 100 insertions(+), 69 deletions(-)
> >>>
> >>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> >>> index f0abc38c40a..cd64b2bc12d 100644
> >>> --- a/arch/loongarch/Kconfig
> >>> +++ b/arch/loongarch/Kconfig
> >>> @@ -9,6 +9,7 @@ config LOONGARCH
> >>>        select ACPI_PPTT if ACPI
> >>>        select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> >>>        select ARCH_BINFMT_ELF_STATE
> >>> +     select ARCH_DEFER_KASAN if KASAN
> >>
> >> Instead of adding 'if KASAN' in all users, you could do in two steps:
> >>
> >> Add a symbol ARCH_NEEDS_DEFER_KASAN.
> >>
> >> +config ARCH_NEEDS_DEFER_KASAN
> >> +       bool
> >>
> >> And then:
> >>
> >> +config ARCH_DEFER_KASAN
> >> +       def_bool
> >> +       depends on KASAN
> >> +       depends on ARCH_DEFER_KASAN
> >> +       help
> >> +         Architectures should select this if they need to defer KASAN
> >> +         initialization until shadow memory is properly set up. This
> >> +         enables runtime control via static keys. Otherwise, KASAN uses
> >> +         compile-time constants for better performance.
> >>
> >
> > Actually, I don't see the benefits from this option. Sorry, have just
> > revisited this again.
> > With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
> > 2 options:
> >
> > select ARCH_NEEDS_DEFER_KASAN
> > select ARCH_DEFER_KASAN
>
> Sorry, my mistake, ARCH_DEFER_KASAN has to be 'def_bool y'. Missing the
> 'y'. That way it is automatically set to 'y' as long as KASAN and
> ARCH_NEEDS_DEFER_KASAN are selected. Should be:
>
> config ARCH_DEFER_KASAN
>         def_bool y
>         depends on KASAN
>         depends on ARCH_NEEDS_DEFER_KASAN
>
>
> >
> > and the oneline with `if` condition is cleaner.
> > select ARCH_DEFER_KASAN if KASAN

Hello,

Have just had a chance to test this.

lib/Kconfig.kasan:
        config ARCH_NEEDS_DEFER_KASAN
                bool

        config ARCH_DEFER_KASAN
                def_bool y
                depends on KASAN
                depends on ARCH_NEEDS_DEFER_KASAN

It works for UML defconfig where arch/um/Kconfig is:

config UML
        bool
        default y
        select ARCH_NEEDS_DEFER_KASAN
        select ARCH_DEFER_KASAN if STATIC_LINK

But it prints warnings for PowerPC, LoongArch:

config LOONGARCH
        bool
        ...
        select ARCH_NEEDS_DEFER_KASAN
        select ARCH_DEFER_KASAN

$ make defconfig ARCH=loongarch
*** Default configuration is based on 'loongson3_defconfig'

WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
  Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
  Selected by [y]:
  - LOONGARCH [=y]


config PPC
        bool
        default y
        select ARCH_DEFER_KASAN if PPC_RADIX_MMU
        select ARCH_NEEDS_DEFER_KASAN

$ make ppc64_defconfig

WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
  Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
  Selected by [y]:
  - PPC [=y] && PPC_RADIX_MMU [=y]


> >
>
> I don't think so because it requires all architectures to add 'if KASAN'
> which is not convenient.
>
> Christophe

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Sabyrzhan Tasbolatov 1 month, 3 weeks ago

On Sun, Aug 10, 2025 at 12:20 PM Sabyrzhan Tasbolatov
<snovitoll@gmail.com> wrote:
>
> On Fri, Aug 8, 2025 at 10:03 PM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
> >
> >
> >
> > Le 08/08/2025 à 17:33, Sabyrzhan Tasbolatov a écrit :
> > > On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> > > <christophe.leroy@csgroup.eu> wrote:
> > >>
> > >>
> > >>
> > >> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> > >>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> > >>> to defer KASAN initialization until shadow memory is properly set up,
> > >>> and unify the static key infrastructure across all KASAN modes.
> > >>
> > >> That probably desserves more details, maybe copy in informations from
> > >> the top of cover letter.
> > >>
> > >> I think there should also be some exeplanations about
> > >> kasan_arch_is_ready() becoming kasan_enabled(), and also why
> > >> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
> > >> without being replaced by kasan_enabled().
> > >>
> > >>>
> > >>> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> > >>>
> > >>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D217049&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe4f5a759ad6452b047408ddd691024a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638902640503259176%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UM4uvQihJdeWwcC6DIiJXbn4wGsrijjRcHc55uCMErI%3D&reserved=0
> > >>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> > >>> ---
> > >>> Changes in v5:
> > >>> - Unified patches where arch (powerpc, UML, loongarch) selects
> > >>>     ARCH_DEFER_KASAN in the first patch not to break
> > >>>     bisectability
> > >>> - Removed kasan_arch_is_ready completely as there is no user
> > >>> - Removed __wrappers in v4, left only those where it's necessary
> > >>>     due to different implementations
> > >>>
> > >>> Changes in v4:
> > >>> - Fixed HW_TAGS static key functionality (was broken in v3)
> > >>> - Merged configuration and implementation for atomicity
> > >>> ---
> > >>>    arch/loongarch/Kconfig                 |  1 +
> > >>>    arch/loongarch/include/asm/kasan.h     |  7 ------
> > >>>    arch/loongarch/mm/kasan_init.c         |  8 +++----
> > >>>    arch/powerpc/Kconfig                   |  1 +
> > >>>    arch/powerpc/include/asm/kasan.h       | 12 ----------
> > >>>    arch/powerpc/mm/kasan/init_32.c        |  2 +-
> > >>>    arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
> > >>>    arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
> > >>>    arch/um/Kconfig                        |  1 +
> > >>>    arch/um/include/asm/kasan.h            |  5 ++--
> > >>>    arch/um/kernel/mem.c                   | 10 ++++++--
> > >>>    include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
> > >>>    include/linux/kasan.h                  |  6 +++++
> > >>>    lib/Kconfig.kasan                      |  8 +++++++
> > >>>    mm/kasan/common.c                      | 17 ++++++++++----
> > >>>    mm/kasan/generic.c                     | 19 +++++++++++----
> > >>>    mm/kasan/hw_tags.c                     |  9 +-------
> > >>>    mm/kasan/kasan.h                       |  8 ++++++-
> > >>>    mm/kasan/shadow.c                      | 12 +++++-----
> > >>>    mm/kasan/sw_tags.c                     |  1 +
> > >>>    mm/kasan/tags.c                        |  2 +-
> > >>>    21 files changed, 100 insertions(+), 69 deletions(-)
> > >>>
> > >>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > >>> index f0abc38c40a..cd64b2bc12d 100644
> > >>> --- a/arch/loongarch/Kconfig
> > >>> +++ b/arch/loongarch/Kconfig
> > >>> @@ -9,6 +9,7 @@ config LOONGARCH
> > >>>        select ACPI_PPTT if ACPI
> > >>>        select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> > >>>        select ARCH_BINFMT_ELF_STATE
> > >>> +     select ARCH_DEFER_KASAN if KASAN
> > >>
> > >> Instead of adding 'if KASAN' in all users, you could do in two steps:
> > >>
> > >> Add a symbol ARCH_NEEDS_DEFER_KASAN.
> > >>
> > >> +config ARCH_NEEDS_DEFER_KASAN
> > >> +       bool
> > >>
> > >> And then:
> > >>
> > >> +config ARCH_DEFER_KASAN
> > >> +       def_bool
> > >> +       depends on KASAN
> > >> +       depends on ARCH_DEFER_KASAN
> > >> +       help
> > >> +         Architectures should select this if they need to defer KASAN
> > >> +         initialization until shadow memory is properly set up. This
> > >> +         enables runtime control via static keys. Otherwise, KASAN uses
> > >> +         compile-time constants for better performance.
> > >>
> > >
> > > Actually, I don't see the benefits from this option. Sorry, have just
> > > revisited this again.
> > > With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
> > > 2 options:
> > >
> > > select ARCH_NEEDS_DEFER_KASAN
> > > select ARCH_DEFER_KASAN
> >
> > Sorry, my mistake, ARCH_DEFER_KASAN has to be 'def_bool y'. Missing the
> > 'y'. That way it is automatically set to 'y' as long as KASAN and
> > ARCH_NEEDS_DEFER_KASAN are selected. Should be:
> >
> > config ARCH_DEFER_KASAN
> >         def_bool y
> >         depends on KASAN
> >         depends on ARCH_NEEDS_DEFER_KASAN
> >
> >
> > >
> > > and the oneline with `if` condition is cleaner.
> > > select ARCH_DEFER_KASAN if KASAN
>
> Hello,
>
> Have just had a chance to test this.
>
> lib/Kconfig.kasan:
>         config ARCH_NEEDS_DEFER_KASAN
>                 bool
>
>         config ARCH_DEFER_KASAN
>                 def_bool y
>                 depends on KASAN
>                 depends on ARCH_NEEDS_DEFER_KASAN

Setting Kconfig.kasan without KASAN works fine for 3 arch that selects
ARCH_DEFER_KASAN:

config ARCH_DEFER_KASAN
       def_bool y
       depends on ARCH_NEEDS_DEFER_KASAN

Going to send v6 soon.

P.S.: Fixed email of David Gow.

>
> It works for UML defconfig where arch/um/Kconfig is:
>
> config UML
>         bool
>         default y
>         select ARCH_NEEDS_DEFER_KASAN
>         select ARCH_DEFER_KASAN if STATIC_LINK
>
> But it prints warnings for PowerPC, LoongArch:
>
> config LOONGARCH
>         bool
>         ...
>         select ARCH_NEEDS_DEFER_KASAN
>         select ARCH_DEFER_KASAN
>
> $ make defconfig ARCH=loongarch
> *** Default configuration is based on 'loongson3_defconfig'
>
> WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
>   Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
>   Selected by [y]:
>   - LOONGARCH [=y]
>
>
> config PPC
>         bool
>         default y
>         select ARCH_DEFER_KASAN if PPC_RADIX_MMU
>         select ARCH_NEEDS_DEFER_KASAN
>
> $ make ppc64_defconfig
>
> WARNING: unmet direct dependencies detected for ARCH_DEFER_KASAN
>   Depends on [n]: KASAN [=n] && ARCH_NEEDS_DEFER_KASAN [=y]
>   Selected by [y]:
>   - PPC [=y] && PPC_RADIX_MMU [=y]
>
>
> > >
> >
> > I don't think so because it requires all architectures to add 'if KASAN'
> > which is not convenient.
> >
> > Christophe

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Sabyrzhan Tasbolatov 1 month, 3 weeks ago

On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
> > Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
> > to defer KASAN initialization until shadow memory is properly set up,
> > and unify the static key infrastructure across all KASAN modes.
>
> That probably desserves more details, maybe copy in informations from
> the top of cover letter.
>
> I think there should also be some exeplanations about
> kasan_arch_is_ready() becoming kasan_enabled(), and also why
> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
> without being replaced by kasan_enabled().

I will try to explain in details in this git commit message. Will copy this part
from my cover letter as well. Hopefully, this below is concise yet
informative description:

        The core issue is that different architectures have
inconsistent approaches
        to KASAN readiness tracking:
        - PowerPC, LoongArch, and UML arch, each implement own
kasan_arch_is_ready()
        - Only HW_TAGS mode had a unified static key (kasan_flag_enabled)
        - Generic and SW_TAGS modes relied on arch-specific solutions
        or always-on behavior

        This patch addresses the fragmentation in KASAN initialization
        across architectures by introducing a unified approach that eliminates
        duplicate static keys and arch-specific kasan_arch_is_ready()
        implementations.

        Let's replace kasan_arch_is_ready() with existing kasan_enabled() check,
        which examines the static key being enabled if arch selects
        ARCH_DEFER_KASAN or has HW_TAGS mode support.
        For other arch, kasan_enabled() checks the enablement during
compile time.

        Now KASAN users can use a single kasan_enabled() check everywhere.

>
> >
> > [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
> >
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> > ---
> > Changes in v5:
> > - Unified patches where arch (powerpc, UML, loongarch) selects
> >    ARCH_DEFER_KASAN in the first patch not to break
> >    bisectability
> > - Removed kasan_arch_is_ready completely as there is no user
> > - Removed __wrappers in v4, left only those where it's necessary
> >    due to different implementations
> >
> > Changes in v4:
> > - Fixed HW_TAGS static key functionality (was broken in v3)
> > - Merged configuration and implementation for atomicity
> > ---
> >   arch/loongarch/Kconfig                 |  1 +
> >   arch/loongarch/include/asm/kasan.h     |  7 ------
> >   arch/loongarch/mm/kasan_init.c         |  8 +++----
> >   arch/powerpc/Kconfig                   |  1 +
> >   arch/powerpc/include/asm/kasan.h       | 12 ----------
> >   arch/powerpc/mm/kasan/init_32.c        |  2 +-
> >   arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
> >   arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
> >   arch/um/Kconfig                        |  1 +
> >   arch/um/include/asm/kasan.h            |  5 ++--
> >   arch/um/kernel/mem.c                   | 10 ++++++--
> >   include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
> >   include/linux/kasan.h                  |  6 +++++
> >   lib/Kconfig.kasan                      |  8 +++++++
> >   mm/kasan/common.c                      | 17 ++++++++++----
> >   mm/kasan/generic.c                     | 19 +++++++++++----
> >   mm/kasan/hw_tags.c                     |  9 +-------
> >   mm/kasan/kasan.h                       |  8 ++++++-
> >   mm/kasan/shadow.c                      | 12 +++++-----
> >   mm/kasan/sw_tags.c                     |  1 +
> >   mm/kasan/tags.c                        |  2 +-
> >   21 files changed, 100 insertions(+), 69 deletions(-)
> >
> > diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > index f0abc38c40a..cd64b2bc12d 100644
> > --- a/arch/loongarch/Kconfig
> > +++ b/arch/loongarch/Kconfig
> > @@ -9,6 +9,7 @@ config LOONGARCH
> >       select ACPI_PPTT if ACPI
> >       select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> >       select ARCH_BINFMT_ELF_STATE
> > +     select ARCH_DEFER_KASAN if KASAN
>
> Instead of adding 'if KASAN' in all users, you could do in two steps:
>
> Add a symbol ARCH_NEEDS_DEFER_KASAN.
>
> +config ARCH_NEEDS_DEFER_KASAN
> +       bool
>
> And then:
>
> +config ARCH_DEFER_KASAN
> +       def_bool
> +       depends on KASAN
> +       depends on ARCH_DEFER_KASAN
> +       help
> +         Architectures should select this if they need to defer KASAN
> +         initialization until shadow memory is properly set up. This
> +         enables runtime control via static keys. Otherwise, KASAN uses
> +         compile-time constants for better performance.
>

Thanks, will do it in v6 (during weekends though as I'm away from my PC)
unless anyone has objections to it.

FYI, I see that Andrew added yesterday v5 to mm-new:
https://lore.kernel.org/all/20250807222945.61E0AC4CEEB@smtp.kernel.org/
https://lore.kernel.org/all/20250807222941.88655C4CEEB@smtp.kernel.org/

Andrey Ryabinin, could you please also review if all comments are
addressed in v5?
So I could work on anything new in v6 during these weekends.

>
>
> >       select ARCH_DISABLE_KASAN_INLINE
> >       select ARCH_ENABLE_MEMORY_HOTPLUG
> >       select ARCH_ENABLE_MEMORY_HOTREMOVE
> > diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
> > index 62f139a9c87..0e50e5b5e05 100644
> > --- a/arch/loongarch/include/asm/kasan.h
> > +++ b/arch/loongarch/include/asm/kasan.h
> > @@ -66,7 +66,6 @@
> >   #define XKPRANGE_WC_SHADOW_OFFSET   (KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
> >   #define XKVRANGE_VC_SHADOW_OFFSET   (KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
> >
> > -extern bool kasan_early_stage;
> >   extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
> >
> >   #define kasan_mem_to_shadow kasan_mem_to_shadow
> > @@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
> >   #define kasan_shadow_to_mem kasan_shadow_to_mem
> >   const void *kasan_shadow_to_mem(const void *shadow_addr);
> >
> > -#define kasan_arch_is_ready kasan_arch_is_ready
> > -static __always_inline bool kasan_arch_is_ready(void)
> > -{
> > -     return !kasan_early_stage;
> > -}
> > -
> >   #define addr_has_metadata addr_has_metadata
> >   static __always_inline bool addr_has_metadata(const void *addr)
> >   {
> > diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> > index d2681272d8f..170da98ad4f 100644
> > --- a/arch/loongarch/mm/kasan_init.c
> > +++ b/arch/loongarch/mm/kasan_init.c
> > @@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> >   #define __pte_none(early, pte) (early ? pte_none(pte) : \
> >   ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
> >
> > -bool kasan_early_stage = true;
> > -
> >   void *kasan_mem_to_shadow(const void *addr)
> >   {
> > -     if (!kasan_arch_is_ready()) {
> > +     if (!kasan_enabled()) {
> >               return (void *)(kasan_early_shadow_page);
> >       } else {
> >               unsigned long maddr = (unsigned long)addr;
> > @@ -298,7 +296,8 @@ void __init kasan_init(void)
> >       kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> >                                       kasan_mem_to_shadow((void *)KFENCE_AREA_END));
> >
> > -     kasan_early_stage = false;
> > +     /* Enable KASAN here before kasan_mem_to_shadow(). */
> > +     kasan_init_generic();
> >
> >       /* Populate the linear mapping */
> >       for_each_mem_range(i, &pa_start, &pa_end) {
> > @@ -329,5 +328,4 @@ void __init kasan_init(void)
> >
> >       /* At this point kasan is fully initialized. Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KernelAddressSanitizer initialized.\n");
> >   }
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 93402a1d9c9..a324dcdb8eb 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -122,6 +122,7 @@ config PPC
> >       # Please keep this list sorted alphabetically.
> >       #
> >       select ARCH_32BIT_OFF_T if PPC32
> > +     select ARCH_DEFER_KASAN                 if KASAN && PPC_RADIX_MMU
> >       select ARCH_DISABLE_KASAN_INLINE        if PPC_RADIX_MMU
> >       select ARCH_DMA_DEFAULT_COHERENT        if !NOT_COHERENT_CACHE
> >       select ARCH_ENABLE_MEMORY_HOTPLUG
> > diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h
> > index b5bbb94c51f..957a57c1db5 100644
> > --- a/arch/powerpc/include/asm/kasan.h
> > +++ b/arch/powerpc/include/asm/kasan.h
> > @@ -53,18 +53,6 @@
> >   #endif
> >
> >   #ifdef CONFIG_KASAN
> > -#ifdef CONFIG_PPC_BOOK3S_64
> > -DECLARE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> > -
> > -static __always_inline bool kasan_arch_is_ready(void)
> > -{
> > -     if (static_branch_likely(&powerpc_kasan_enabled_key))
> > -             return true;
> > -     return false;
> > -}
> > -
> > -#define kasan_arch_is_ready kasan_arch_is_ready
> > -#endif
> >
> >   void kasan_early_init(void);
> >   void kasan_mmu_init(void);
> > diff --git a/arch/powerpc/mm/kasan/init_32.c b/arch/powerpc/mm/kasan/init_32.c
> > index 03666d790a5..1d083597464 100644
> > --- a/arch/powerpc/mm/kasan/init_32.c
> > +++ b/arch/powerpc/mm/kasan/init_32.c
> > @@ -165,7 +165,7 @@ void __init kasan_init(void)
> >
> >       /* At this point kasan is fully initialized. Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_late_init(void)
> > diff --git a/arch/powerpc/mm/kasan/init_book3e_64.c b/arch/powerpc/mm/kasan/init_book3e_64.c
> > index 60c78aac0f6..0d3a73d6d4b 100644
> > --- a/arch/powerpc/mm/kasan/init_book3e_64.c
> > +++ b/arch/powerpc/mm/kasan/init_book3e_64.c
> > @@ -127,7 +127,7 @@ void __init kasan_init(void)
> >
> >       /* Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_late_init(void) { }
> > diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
> > index 7d959544c07..dcafa641804 100644
> > --- a/arch/powerpc/mm/kasan/init_book3s_64.c
> > +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
> > @@ -19,8 +19,6 @@
> >   #include <linux/memblock.h>
> >   #include <asm/pgalloc.h>
> >
> > -DEFINE_STATIC_KEY_FALSE(powerpc_kasan_enabled_key);
> > -
> >   static void __init kasan_init_phys_region(void *start, void *end)
> >   {
> >       unsigned long k_start, k_end, k_cur;
> > @@ -92,11 +90,9 @@ void __init kasan_init(void)
> >        */
> >       memset(kasan_early_shadow_page, 0, PAGE_SIZE);
> >
> > -     static_branch_inc(&powerpc_kasan_enabled_key);
> > -
> >       /* Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KASAN init done\n");
> > +     kasan_init_generic();
> >   }
> >
> >   void __init kasan_early_init(void) { }
> > diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> > index 9083bfdb773..a12cc072ab1 100644
> > --- a/arch/um/Kconfig
> > +++ b/arch/um/Kconfig
> > @@ -5,6 +5,7 @@ menu "UML-specific options"
> >   config UML
> >       bool
> >       default y
> > +     select ARCH_DEFER_KASAN if STATIC_LINK
>
> No need to also verify KASAN here like powerpc and loongarch ?

Sorry, I didn't quite understand the question.
I've verified powerpc with KASAN enabled which selects KASAN_OUTLINE,
as far as I remember, and GENERIC mode.

I haven't tested LoongArch booting via QEMU, only tested compilation.
I guess, I need to test the boot, will try to learn how to do it for
qemu-system-loongarch64. Would be helpful LoongArch devs in CC can
assist as well.

STATIC_LINK is defined for UML only.

>
> >       select ARCH_WANTS_DYNAMIC_TASK_STRUCT
> >       select ARCH_HAS_CACHE_LINE_SIZE
> >       select ARCH_HAS_CPU_FINALIZE_INIT
> > diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
> > index f97bb1f7b85..b54a4e937fd 100644
> > --- a/arch/um/include/asm/kasan.h
> > +++ b/arch/um/include/asm/kasan.h
> > @@ -24,10 +24,9 @@
> >
> >   #ifdef CONFIG_KASAN
> >   void kasan_init(void);
> > -extern int kasan_um_is_ready;
> >
> > -#ifdef CONFIG_STATIC_LINK
> > -#define kasan_arch_is_ready() (kasan_um_is_ready)
> > +#if defined(CONFIG_STATIC_LINK) && defined(CONFIG_KASAN_INLINE)
> > +#error UML does not work in KASAN_INLINE mode with STATIC_LINK enabled!
> >   #endif
> >   #else
> >   static inline void kasan_init(void) { }
> > diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
> > index 76bec7de81b..261fdcd21be 100644
> > --- a/arch/um/kernel/mem.c
> > +++ b/arch/um/kernel/mem.c
> > @@ -21,9 +21,9 @@
> >   #include <os.h>
> >   #include <um_malloc.h>
> >   #include <linux/sched/task.h>
> > +#include <linux/kasan.h>
> >
> >   #ifdef CONFIG_KASAN
> > -int kasan_um_is_ready;
> >   void kasan_init(void)
> >   {
> >       /*
> > @@ -32,7 +32,10 @@ void kasan_init(void)
> >        */
> >       kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
> >       init_task.kasan_depth = 0;
> > -     kasan_um_is_ready = true;
> > +     /* Since kasan_init() is called before main(),
> > +      * KASAN is initialized but the enablement is deferred after
> > +      * jump_label_init(). See arch_mm_preinit().
> > +      */
>
> Format standard is different outside network, see:
> https://docs.kernel.org/process/coding-style.html#commenting

Thanks! Will do in v6.

>
> >   }
> >
> >   static void (*kasan_init_ptr)(void)
> > @@ -58,6 +61,9 @@ static unsigned long brk_end;
> >
> >   void __init arch_mm_preinit(void)
> >   {
> > +     /* Safe to call after jump_label_init(). Enables KASAN. */
> > +     kasan_init_generic();
> > +
> >       /* clear the zero-page */
> >       memset(empty_zero_page, 0, PAGE_SIZE);
> >
> > diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> > index 6f612d69ea0..9eca967d852 100644
> > --- a/include/linux/kasan-enabled.h
> > +++ b/include/linux/kasan-enabled.h
> > @@ -4,32 +4,46 @@
> >
> >   #include <linux/static_key.h>
> >
> > -#ifdef CONFIG_KASAN_HW_TAGS
> > -
> > +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> > +/*
> > + * Global runtime flag for KASAN modes that need runtime control.
> > + * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode.
> > + */
> >   DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> >
> > +/*
> > + * Runtime control for shadow memory initialization or HW_TAGS mode.
> > + * Uses static key for architectures that need deferred KASAN or HW_TAGS.
> > + */
> >   static __always_inline bool kasan_enabled(void)
> >   {
> >       return static_branch_likely(&kasan_flag_enabled);
> >   }
> >
> > -static inline bool kasan_hw_tags_enabled(void)
> > +static inline void kasan_enable(void)
> >   {
> > -     return kasan_enabled();
> > +     static_branch_enable(&kasan_flag_enabled);
> >   }
> > -
> > -#else /* CONFIG_KASAN_HW_TAGS */
> > -
> > -static inline bool kasan_enabled(void)
> > +#else
> > +/* For architectures that can enable KASAN early, use compile-time check. */
> > +static __always_inline bool kasan_enabled(void)
> >   {
> >       return IS_ENABLED(CONFIG_KASAN);
> >   }
> >
> > +static inline void kasan_enable(void) {}
> > +#endif /* CONFIG_ARCH_DEFER_KASAN || CONFIG_KASAN_HW_TAGS */
> > +
> > +#ifdef CONFIG_KASAN_HW_TAGS
> > +static inline bool kasan_hw_tags_enabled(void)
> > +{
> > +     return kasan_enabled();
> > +}
> > +#else
> >   static inline bool kasan_hw_tags_enabled(void)
> >   {
> >       return false;
> >   }
> > -
> >   #endif /* CONFIG_KASAN_HW_TAGS */
> >
> >   #endif /* LINUX_KASAN_ENABLED_H */
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index 890011071f2..51a8293d1af 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -543,6 +543,12 @@ void kasan_report_async(void);
> >
> >   #endif /* CONFIG_KASAN_HW_TAGS */
> >
> > +#ifdef CONFIG_KASAN_GENERIC
> > +void __init kasan_init_generic(void);
> > +#else
> > +static inline void kasan_init_generic(void) { }
> > +#endif
> > +
> >   #ifdef CONFIG_KASAN_SW_TAGS
> >   void __init kasan_init_sw_tags(void);
> >   #else
> > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> > index f82889a830f..38456560c85 100644
> > --- a/lib/Kconfig.kasan
> > +++ b/lib/Kconfig.kasan
> > @@ -19,6 +19,14 @@ config ARCH_DISABLE_KASAN_INLINE
> >         Disables both inline and stack instrumentation. Selected by
> >         architectures that do not support these instrumentation types.
> >
> > +config ARCH_DEFER_KASAN
> > +     bool
> > +     help
> > +       Architectures should select this if they need to defer KASAN
> > +       initialization until shadow memory is properly set up. This
> > +       enables runtime control via static keys. Otherwise, KASAN uses
> > +       compile-time constants for better performance.
> > +
> >   config CC_HAS_KASAN_GENERIC
> >       def_bool $(cc-option, -fsanitize=kernel-address)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 9142964ab9c..d9d389870a2 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -32,6 +32,15 @@
> >   #include "kasan.h"
> >   #include "../slab.h"
> >
> > +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS)
> > +/*
> > + * Definition of the unified static key declared in kasan-enabled.h.
> > + * This provides consistent runtime enable/disable across KASAN modes.
> > + */
> > +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> > +EXPORT_SYMBOL(kasan_flag_enabled);
>
> Shouldn't new exports be GPL ?

Hmm, I did it as it's currently EXPORT_SYMBOL for HW_TAGS
https://elixir.bootlin.com/linux/v6.16/source/mm/kasan/hw_tags.c#L53

but I see that in the same HW_TAGS file we have
        EXPORT_SYMBOL_GPL(kasan_flag_vmalloc);

So I guess, we should also export kasan_flag_enabled as EXPORT_SYMBOL_GPL.
Will do in v6.

>
> > +#endif
> > +
> >   struct slab *kasan_addr_to_slab(const void *addr)
> >   {
> >       if (virt_addr_valid(addr))
> > @@ -246,7 +255,7 @@ static inline void poison_slab_object(struct kmem_cache *cache, void *object,
> >   bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
> >                               unsigned long ip)
> >   {
> > -     if (!kasan_arch_is_ready() || is_kfence_address(object))
> > +     if (is_kfence_address(object))
>
> Here and below, no need to replace kasan_arch_is_ready() by
> kasan_enabled() ?

Both functions have __wrappers in include/linux/kasan.h [1],
where there's already kasan_enabled() check. Since we've replaced
kasan_arch_is_ready() with kasan_enabled(), these checks are not needed here.

[1] https://elixir.bootlin.com/linux/v6.16/source/include/linux/kasan.h#L197

>
> >               return false;
> >       return check_slab_allocation(cache, object, ip);
> >   }
> > @@ -254,7 +263,7 @@ bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object,
> >   bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
> >                      bool still_accessible)
> >   {
> > -     if (!kasan_arch_is_ready() || is_kfence_address(object))
> > +     if (is_kfence_address(object))
> >               return false;
> >
> >       /*
> > @@ -293,7 +302,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
> >
> >   static inline bool check_page_allocation(void *ptr, unsigned long ip)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return false;
> >
> >       if (ptr != page_address(virt_to_head_page(ptr))) {
> > @@ -522,7 +531,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
> >               return true;
> >       }
> >
> > -     if (is_kfence_address(ptr) || !kasan_arch_is_ready())
> > +     if (is_kfence_address(ptr))
> >               return true;
> >
> >       slab = folio_slab(folio);
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index d54e89f8c3e..b413c46b3e0 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -36,6 +36,17 @@
> >   #include "kasan.h"
> >   #include "../slab.h"
> >
> > +/*
> > + * Initialize Generic KASAN and enable runtime checks.
> > + * This should be called from arch kasan_init() once shadow memory is ready.
> > + */
> > +void __init kasan_init_generic(void)
> > +{
> > +     kasan_enable();
> > +
> > +     pr_info("KernelAddressSanitizer initialized (generic)\n");
> > +}
> > +
> >   /*
> >    * All functions below always inlined so compiler could
> >    * perform better optimizations in each of __asan_loadX/__assn_storeX
> > @@ -165,7 +176,7 @@ static __always_inline bool check_region_inline(const void *addr,
> >                                               size_t size, bool write,
> >                                               unsigned long ret_ip)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return true;
> >
> >       if (unlikely(size == 0))
> > @@ -193,7 +204,7 @@ bool kasan_byte_accessible(const void *addr)
> >   {
> >       s8 shadow_byte;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return true;
> >
> >       shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
> > @@ -495,7 +506,7 @@ static void release_alloc_meta(struct kasan_alloc_meta *meta)
> >
> >   static void release_free_meta(const void *object, struct kasan_free_meta *meta)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       /* Check if free meta is valid. */
> > @@ -562,7 +573,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> >       kasan_save_track(&alloc_meta->alloc_track, flags);
> >   }
> >
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
> >   {
> >       struct kasan_free_meta *free_meta;
> >
> > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> > index 9a6927394b5..c8289a3feab 100644
> > --- a/mm/kasan/hw_tags.c
> > +++ b/mm/kasan/hw_tags.c
> > @@ -45,13 +45,6 @@ static enum kasan_arg kasan_arg __ro_after_init;
> >   static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
> >   static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
> >
> > -/*
> > - * Whether KASAN is enabled at all.
> > - * The value remains false until KASAN is initialized by kasan_init_hw_tags().
> > - */
> > -DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
> > -EXPORT_SYMBOL(kasan_flag_enabled);
> > -
> >   /*
> >    * Whether the selected mode is synchronous, asynchronous, or asymmetric.
> >    * Defaults to KASAN_MODE_SYNC.
> > @@ -260,7 +253,7 @@ void __init kasan_init_hw_tags(void)
> >       kasan_init_tags();
> >
> >       /* KASAN is now initialized, enable it. */
> > -     static_branch_enable(&kasan_flag_enabled);
> > +     kasan_enable();
> >
> >       pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
> >               kasan_mode_info(),
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index 129178be5e6..8a9d8a6ea71 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -398,7 +398,13 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
> >   void kasan_set_track(struct kasan_track *track, depot_stack_handle_t stack);
> >   void kasan_save_track(struct kasan_track *track, gfp_t flags);
> >   void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object);
> > +
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object);
> > +static inline void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +{
> > +     if (kasan_enabled())
> > +             __kasan_save_free_info(cache, object);
> > +}
> >
> >   #ifdef CONFIG_KASAN_GENERIC
> >   bool kasan_quarantine_put(struct kmem_cache *cache, void *object);
> > diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> > index d2c70cd2afb..2e126cb21b6 100644
> > --- a/mm/kasan/shadow.c
> > +++ b/mm/kasan/shadow.c
> > @@ -125,7 +125,7 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
> >   {
> >       void *shadow_start, *shadow_end;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       /*
> > @@ -150,7 +150,7 @@ EXPORT_SYMBOL_GPL(kasan_poison);
> >   #ifdef CONFIG_KASAN_GENERIC
> >   void kasan_poison_last_granule(const void *addr, size_t size)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       if (size & KASAN_GRANULE_MASK) {
> > @@ -390,7 +390,7 @@ int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
> >       unsigned long shadow_start, shadow_end;
> >       int ret;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return 0;
> >
> >       if (!is_vmalloc_or_module_addr((void *)addr))
> > @@ -560,7 +560,7 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
> >       unsigned long region_start, region_end;
> >       unsigned long size;
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
> > @@ -611,7 +611,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> >        * with setting memory tags, so the KASAN_VMALLOC_INIT flag is ignored.
> >        */
> >
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return (void *)start;
> >
> >       if (!is_vmalloc_or_module_addr(start))
> > @@ -636,7 +636,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> >    */
> >   void __kasan_poison_vmalloc(const void *start, unsigned long size)
> >   {
> > -     if (!kasan_arch_is_ready())
> > +     if (!kasan_enabled())
> >               return;
> >
> >       if (!is_vmalloc_or_module_addr(start))
> > diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> > index b9382b5b6a3..c75741a7460 100644
> > --- a/mm/kasan/sw_tags.c
> > +++ b/mm/kasan/sw_tags.c
> > @@ -44,6 +44,7 @@ void __init kasan_init_sw_tags(void)
> >               per_cpu(prng_state, cpu) = (u32)get_cycles();
> >
> >       kasan_init_tags();
> > +     kasan_enable();
> >
> >       pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n",
> >               str_on_off(kasan_stack_collection_enabled()));
> > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> > index d65d48b85f9..b9f31293622 100644
> > --- a/mm/kasan/tags.c
> > +++ b/mm/kasan/tags.c
> > @@ -142,7 +142,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> >       save_stack_info(cache, object, flags, false);
> >   }
> >
> > -void kasan_save_free_info(struct kmem_cache *cache, void *object)
> > +void __kasan_save_free_info(struct kmem_cache *cache, void *object)
> >   {
> >       save_stack_info(cache, object, 0, true);
> >   }
>

Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

Posted by Christophe Leroy 1 month, 3 weeks ago


Le 08/08/2025 à 09:26, Sabyrzhan Tasbolatov a écrit :
> On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>>> diff --git a/arch/um/Kconfig b/arch/um/Kconfig
>>> index 9083bfdb773..a12cc072ab1 100644
>>> --- a/arch/um/Kconfig
>>> +++ b/arch/um/Kconfig
>>> @@ -5,6 +5,7 @@ menu "UML-specific options"
>>>    config UML
>>>        bool
>>>        default y
>>> +     select ARCH_DEFER_KASAN if STATIC_LINK
>>
>> No need to also verify KASAN here like powerpc and loongarch ?
> 
> Sorry, I didn't quite understand the question.
> I've verified powerpc with KASAN enabled which selects KASAN_OUTLINE,
> as far as I remember, and GENERIC mode.

The question is whether:

	select ARCH_DEFER_KASAN if STATIC_LINK

is enough ? Shouldn't it be:

	select ARCH_DEFER_KASAN if KASAN && STATIC_LINK

Like for powerpc and loongarch ?


> 
> I haven't tested LoongArch booting via QEMU, only tested compilation.
> I guess, I need to test the boot, will try to learn how to do it for
> qemu-system-loongarch64. Would be helpful LoongArch devs in CC can
> assist as well.
> 
> STATIC_LINK is defined for UML only.
>

[PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes
[PATCH v5 2/2] kasan: call kasan_init_generic in kasan_init